Crosslinkable rubber composition and cross-linked rubber

ABSTRACT

A crosslinkable rubber composition comprising 0.2 to 10 parts by weight of an aromatic secondary amine-based anti-aging agent and 0.5 to 20 parts by weight of a polyamine-based crosslinking agent with respect to 100 parts by weight of a nitrile rubber including an α,β-ethylenically unsaturated nitrile unit and an α,β-ethylenically unsaturated dicarboxylic acid monoester unit, and with iodine value of 120 or less. The present invention can provide a crosslinkable rubber composition, providable of a cross-linked rubber excellent in a variety of properties such as mechanical strength and small in compression set, and a cross-linked rubber obtained by cross-linking the rubber composition.

FIELD OF THE INVENTION

The present invention relates to a crosslinkable rubber composition,providable of a cross-linked article excellent in a variety ofproperties such as mechanical strength and small in compression set, anda cross-linked rubber obtained by cross-linking the rubber composition.

DESCRIPTION OF THE RELATED ART

As a rubber having oil resistance, heat resistance and ozone resistance,nitrile group containing highly-saturated copolymer rubber has beenknown, and the cross-linked rubber thereof has been used as a materialfor various automotive rubber products such as a belt, hose, gasket,packing and oil-seal. Recently, it has been required to further improvemechanical strength such as tensile strength and tensile stress, andparticularly in a bulk rubber product other than a fiber impregnatedbody or metal composite body, compression set has been required toimprove as well as mechanical strength such as tensile strength.

In response to this, a crosslinkable rubber composition comprising anitrile group containing highly-saturated copolymer rubber includingα,β-ethylenically unsaturated dicarboxylic acid monoalkyl ester units, apolyamine-based crosslinking agent and a basic crosslinking acceleratorhas been proposed (Patent Article 1). By crosslinking the composition,there can be provided a cross-linked rubber having improved tensilestrength, tensile stress and compression set. However, for example, in across-linked rubber with a structure surrounding a space portion such asO-ring, compression set tends to increase due to an influence of forceat compression, so that further improvement in compression set has beenrequired.

Also, to improve compression set while keeping heat aging resistancefavorably, for example, there have been proposed a method to blendsilica-based inorganic compounding ingredient with pH of 8.5 or more andvinylsilane-based coupling agent (Patent Article 2), and a method toblend additives selected from a group including strong base, a salt ofstrong base and weak acid, carbodiimide, polycarbodiimide and a mixturethereof (Patent Article 3), etc. However, even in the Patent Articles 2and 3, improvement effect in compression set is insufficient, andfurther improvement has yet been required in compression set.

-   Patent Article 1: The Japanese Unexamined Patent Publication    2001-55471;-   Patent Article 2: The Japanese Unexamined Patent Publication    S62-240338-   Patent Article 3: The Japanese Unexamined Patent Publication    H11-293039.

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

An object of the present invention is to provide a crosslinkable rubbercomposition, providable of a cross-linked rubber with particularly smallcompression set while well-maintaining a variety of properties such asmechanical strength, and a cross-linked rubber obtained by cross-linkingthe rubber composition.

Means for Solving the Problem

The present inventors found, as a result of keen examinations, that itis possible to attain the above purpose by a certain crosslinkablerubber composition including a specific nitrile rubber and apolyamine-based crosslinking agent as a crosslinking agent, and came tocomplete the present invention based on the findings.

Namely, according to a first aspect of the present invention,

there is provided a crosslinkable rubber composition comprising 0.2 to10 parts by weight of an aromatic secondary amine-based anti-aging agent(A2) and 0.2 to 20 parts by weight of a polyamine-based crosslinkingagent (A3) with respect to 100 parts by weight of a nitrile rubber (A1)including an α,β-ethylenically unsaturated nitrile monomer unit and anα,β-ethylenically unsaturated dicarboxylic acid monoester monomer unitand having iodine value of 120 or less.

In the first aspect, preferably, a monomer forming saidα,β-ethylenically unsaturated dicarboxylic acid monoester monomer unitis a monoester monomer of a dicarboxylic acid containing a carboxylgroup in each of two carbon atoms forming an α,β-ethylenicallyunsaturated bond.

In the first aspect, preferably, compound Mooney viscosity ML₁₊₄ (100°C.) of said crosslinkable rubber composition is 15 to 200.

In the first aspect, preferably, said crosslinkable rubber compositionprovides a cross-linked rubber, wherein O-ring compression set is 71% orless after maintaining the cross-linked rubber in a 25%-compressed stateat 150° C. for 504 hours.

Alternatively, according to a second aspect of the present invention,

there is provided a crosslinkable rubber composition comprising 0.1 to20 parts by weight of a primary monoamine (B2) having no polar groupother than an amino group and 0.1 to 20 parts by weight of apolyamine-based crosslinking agent (B3) with respect to 100 parts byweight of a nitrile rubber (B1) including an α,β-ethylenicallyunsaturated nitrile monomer unit and an α,β-ethylenically unsaturateddicarboxylic acid monoester monomer unit and having iodine value of 120or less.

In the second aspect, preferably, said primary monoamine (B2) having nopolar group other than an amino group is an aliphatic primary monoamine.

Alternatively, according to a third aspect of the present invention,

there is provided a crosslinkable rubber composition comprising anitrile group containing highly-saturated copolymer rubber (C1), apolyoxyalkylene alkyl ether phosphate ester (C2) and a polyamine-basedcrosslinking agent (C3).

In the third aspect, preferably, said nitrile group containinghighly-saturated copolymer rubber (C1) is a nitrile rubber in which acontent of α,β-ethylenically unsaturated nitrile monomer units is 10 to60 wt % and iodine value is 100 or less.

Alternatively, according to a fourth aspect of the present invention,

there is provided a crosslinkable rubber composition comprising 0.2 to20 parts by weight of a polyamine-based crosslinking agent (D3) withrespect to a total of 100 parts by weight of a nitrile group containinghighly-saturated copolymer rubber (D1) having an α,β-ethylenicallyunsaturated dicarboxylic acid monoester monomer unit and an acrylicrubber (D2) having an α,β-ethylenically unsaturated dicarboxylic acidmonoester monomer unit.

In the fourth aspect, preferably, a monomer forming saidα,β-ethylenically unsaturated dicarboxylic acid monoester monomer unitis a monoester monomer of a dicarboxylic acid having a carboxyl group ineach of two carbon atoms forming an α,β-ethylenically unsaturated bond,and more preferably, a monomer having an alkoxy group with carbon numberof 3 to 8.

In the fourth aspect, preferably, a weight ratio of said nitrile groupcontaining highly-saturated copolymer rubber (D1) and said acrylicrubber (D2) is 5/95 to 95/5.

In the fourth aspect, preferably, said crosslinkable rubber compositionprovides a cross-linked rubber, wherein O-ring compression set is 40% orless after maintaining the cross-linked rubber in a 25%-compressed stateat 150° C. for 168 hours.

In the fourth aspect, preferably, said crosslinkable rubber compositionfurther includes 0.5 to 10 parts by weight of a basic crosslinkingaccelerator (D4).

Also, the present invention provides a cross-linked rubber obtained bycross-linking the crosslinkable rubber composition according to any oneof the above first to fourth aspects. The cross-linked rubber accordingto the present invention (the first to fourth aspects) is preferablyused as a seal material or a belt material.

Effects of the Invention

According to the present invention, there can be provided acrosslinkable rubber composition, providable of a cross-linked rubberwith particularly small compression set while well maintaining a varietyof properties such as mechanical strength, and a cross-linked rubberobtained by cross-linking the rubber composition

Particularly, according to the first aspect of the present invention,there can be provided a crosslinkable rubber composition, providable ofa cross-linked rubber well-balanced in mechanical strength, such astensile strength and tensile stress, and elongation and havingparticularly small compression set, and a cross-linked rubber obtainedby cross-linking the rubber composition.

Also, according to the second aspect of the present invention, there canbe provided a crosslinkable rubber composition, providable of across-linked rubber with small compression set, good in workability andexcellent in scorch stability, and a cross-linked rubber obtained bycross-linking the rubber composition.

According to the third aspect of the present invention, there can beprovided a crosslinkable rubber composition, providable of across-linked rubber excellent in heat aging resistance and havingparticularly small compression set, and a cross-linked rubber obtainedby cross-linking the rubber composition.

Further, according to the fourth aspect of the present invention, therecan be provided a crosslinkable rubber composition, providable of across-linked rubber excellent in mechanical strength and heat resistanceand having significantly small compression set by using a nitrile groupcontaining highly-saturated copolymer rubber, and a cross-linked rubberobtained by cross-linking the rubber composition.

BEST MODE FOR WORKING THE INVENTION First Aspect First Embodiment

First, an embodiment according to the first aspect of the presentinvention, i.e. a first embodiment, will be described.

The crosslinkable rubber composition according to the first aspect ofthe present invention comprises 0.2 to 10 parts by weight of an aromaticsecondary amine-based anti-aging agent (A2) and 0.2 to 20 parts byweight of a polyamine-based crosslinking agent (A3) with respect to 100parts by weight of a nitrile rubber (A1) including an α,β-ethylenicallyunsaturated nitrile monomer unit and an α,β-ethylenically unsaturateddicarboxylic acid monoester monomer unit and having iodine value of 120or less.

Hereinafter, in the first aspect (first embodiment), the nitrile rubber(A1) comprising the above α,β-ethylenically unsaturated dicarboxylicacid monoester monomer unit and having iodine value of 120 or less maybe abbreviated with “nitrile rubber (A1)”.

Nitrile Rubber (A1)

The monomer forming the α,β-ethylenically unsaturated nitrile monomerunit of the nitrile rubber (A1) (α,β-ethylenically unsaturated nitrilemonomer) is not limited as far as it is an α,β-ethylenically unsaturatedcompound having a nitrile group. As the compound, acrylonitrile;α-halogenoacrylonitrile such as α-chloroacrylonitrile andα-bromoacrylonitrile; α-alkylacrylonitrile such as methacrylonitrile;etc., can be mentioned. Among these, acrylonitrile and methacrylonitrileare preferable. As the α,β-ethylenically unsaturated nitrile, aplurality of these may be used.

A content of the α,β-ethylenically unsaturated nitrile monomer unit inthe nitrile rubber (A1) is, preferably 10 to 60 wt %, more preferably 15to 55 wt % and particularly preferably 20 to 50 wt %, per 100 wt % ofthe total monomer units. When the content of the α,β-ethylenicallyunsaturated nitrile monomer unit is too small, oil resistance of theobtained cross-linked rubber may decline; and in contrast, when it istoo large, cold resistance may decline.

The nitrile rubber (A1) comprises the α,β-ethylenically unsaturateddicarboxylic acid monoester monomer unit in addition to theα,β-ethylenically unsaturated nitrile monomer unit. By making theconstitution of the nitrile rubber (A1) comprising the α,β-ethylenicallyunsaturated dicarboxylic acid monoester monomer unit, tensile strengthof the obtained cross-linked rubber tends to be improved.

A preferable method to include the α,β-ethylenically unsaturateddicarboxylic acid monoester monomer unit in the nitrile rubber (A1) mayinclude a method to copolymerize the α,β-ethylenically unsaturateddicarboxylic acid monoester with the above α,β-ethylenically unsaturatednitrile.

As an organic group binding to a carbonyl group through an oxygen atomof the α,β-ethylenically unsaturated dicarboxylic acid monoester, analkyl group, cycloalkyl group and alkylcycloalkyl group may bementioned, and the alkyl group is preferable among them. Carbon numberof the alkyl group is preferably 1 to 10, more preferably 2 to 6. Carbonnumber of the cycloalkyl group is preferably 5 to 12, more preferably 6to 10. Carbon number of the alkylcycloalkyl group is preferably 6 to 12,more preferably 7 to 10. When carbon number of the organic group is toosmall, processing stability of the obtained rubber composition maydecline; and in contrast, when it is too large, cross-linking rate mayslow down and mechanical strength of the cross-linked rubber maydecline.

Examples of the α,β-ethylenically unsaturated dicarboxylic acidmonoester monomer may include a maleate monoalkyl ester such asmonomethyl maleate, monoethyl maleate, monopropyl maleate andmono-n-butyl maleate; a maleate monocycloalkyl ester such asmonocyclopentyl maleate, monocyclohexyl maleate and monocycloheptylmaleate; a maleate monoalkylcycloalkyl ester such as monomethylcyclopentyl maleate and monoethyl cyclohexyl maleate; afumaratemonoalkyl ester such as monomethyl fumarate, monoethyl fumarate,monopropyl fumarate and mono-n-butyl fumarate; a fumarate monocycloalkylester such as monocyclopentyl fumarate, monocyclohexyl fumarate andmonocycloheptyl fumarate; a fumarate monoalkylcycloalkyl ester such asmonomethyl cyclopentyl fumarate and monoethyl cyclohexyl fumarate; acitraconic acid monoalkyl ester such as monomethyl citraconic acid,monoethyl citraconic acid, monopropyl citraconic acid and mono-n-butylcitraconic acid; a citraconic acid monocycloalkyl ester such asmonocyclopentyl citraconic acid, monocyclohexyl citraconic acid andmonocycloheptyl citraconic acid; a citraconic acid monoalkylcycloalkylester such as monomethyl cyclopentyl citraconic acid and monoethylcyclohexyl citraconic acid; an itaconic acid monoalkyl ester such asmonomethyl itaconate, monoethyl itaconate, monopropyl itaconate andmono-n-butyl itaconate; an itaconic acid monocycloalkyl ester such asmonocyclopentyl itaconic acid, monocyclohexyl itaconic acid andmonocycloheptyl itaconic acid; an itaconic acid monoalkylcycloalkylester such as monomethyl cyclopentyl itaconic acid and monoethylcyclohexyl itaconic acid; etc.

Among these, because of their reduction effect of compound Mooneyviscosity ML₁₊₄ (100° C.) of the crosslinkable rubber composition, amonoester (monoalkyl ester, monocycloalkyl ester and monoalkylcycloalkylester) of a dicarboxylic acid having a carboxyl group in each of twocarbon atoms forming an α,β-ethylenically unsaturated bond, such asmaleic acid, fumaric acid and citraconic acid, is preferable, andmonoesters of maleic acid and fumaric acid are particularly preferable.

The content of the α,β-ethylenically unsaturated dicarboxylic acidmonoester monomer unit in the nitrile rubber (A1) is preferably 0.5 to20 wt %, more preferably 1 to 15 wt % and particularly preferably 1.5 to10 wt % per 100 wt % of the total monomer units. When the content of theα,β-ethylenically unsaturated dicarboxylic acid monoester monomer unitof the nitrile rubber (A1) is too small, the cross-link of thecrosslinkable rubber composition may be insufficient. On the other hand,when it is too large, carboxyl groups remaining after the cross-link maycause to reduce resistance to fatigue of the obtained cross-linkedrubber.

The nitrile rubber (A1) normally comprises a diene-based monomer unitand/or α-olefin-based monomer unit in addition to the aboveα,β-ethylenically unsaturated nitrile monomer unit and α,β-ethylenicallyunsaturated dicarboxylic acid monoester monomer unit, so that theobtained cross-linked rubber can be elastic.

As the diene-based monomer forming the diene-based monomer unit, theremay be mentioned a conjugated diene with carbon number of 4 or more suchas 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene and1,3-pentadiene; a nonconjugated diene with carbon number of preferably 5to 12 such as 1,4-pentadiene and 1,4-hexadiene; etc. Among these, theconjugated diene is preferable, and 1,3-butadiene is more preferable.

As the α-olefin-based monomer forming the α-olefin monomer unit, anα-olefin with carbon number of 2 to 12 may be preferable and there maybe exemplified ethylene, propylene, 1-butene, 4-methyl-1-pentene,1-hexene, 1-octene, etc.

A content of the diene-based monomer unit or α-olefin monomer unit inthe nitrile rubber (A1) is preferably 25 to 85 wt %, more preferably 35to 80 wt % and particularly preferably 45 to 75 wt % per 100 wt % of thetotal monomer units. When the content of the unit is too small, rubberelasticity of the obtained cross-linked rubber may decline; and when itis too large, heat resistance and chemical stability may bedeteriorated.

The nitrile rubber (A1) may include other monomer units copolymerizablewith each of the monomers forming the above monomer units, i.e. theα,β-ethylenically unsaturated nitrile monomer, α,β-ethylenicallyunsaturated dicarboxylic acid monoester monomer, and diene-based monomeror α-olefin monomer. As the other monomers, there may be exemplified anα,β-ethylenically unsaturated carboxylic acid ester other than theα,β-ethylenically unsaturated dicarboxylic acid monoester, an aromaticvinyl, a fluorine containing vinyl, an α,β-ethylenically unsaturatedmonocarboxylic acid, an α,β-ethylenically unsaturated polyvalentcarboxylic acid, an α,β-ethylenically unsaturated polyvalent carboxylicanhydride, copolymerizable anti-aging agent, etc.

As the α,β-ethylenically unsaturated carboxylic acid ester other thanthe α,β-ethylenically unsaturated dicarboxylic acid monoester, forexample, there may be mentioned an acrylic acid alkyl ester andmethacrylic acid alkyl ester with carbon number of an alkyl group of 1to 18 such as methyl acrylate, ethyl acrylate, propyl acrylate, butylacrylate, n-dodecyl acrylate, methyl methacrylate and ethylmethacrylate; an acrylic acid alkoxyalkyl ester and methacrylic acidalkoxyalkyl ester with carbon number of an alkoxyalkyl group of 2 to 12such as methoxymethyl acrylate and methoxyethyl methacrylate; an acrylicacid cyanoalkyl ester and methacrylic acid cyanoalkyl ester with carbonnumber of a cyanoalkyl group of 2 to 12 such as α-cyanoethyl acrylate,β-cyanoethyl acrylate and cyanobutyl methacrylate; an acrylic acidhydroxyalkyl ester and methacrylic acid hydroxyalkyl ester with carbonnumber of a hydroxyalkyl group of 1 to 12 such as 2-hydroxyethylacrylate, 2-hydroxyethyl methacrylate and 3-hydroxypropyl acrylate; afluorine-substituted benzyl group containing acrylic acid ester andfluorine-substituted benzyl group containing methacrylic acid ester suchas fluorobenzyl acrylate and fluorobenzyl methacrylate; a fluoroalkylgroup containing acrylic acid ester and fluoroalkyl group containingmethacrylic acid ester such as trifluoroethyl acrylate andtetrafluoropropyl methacrylate; an unsaturated polyvalent carboxylicacid polyalkyl ester such as dimethyl maleate, dimethyl fumarate,dimethyl itaconate and diethyl itaconate; an amino group containingα,β-ethylenically unsaturated carboxylic acid ester such asdimethylaminomethyl acrylate and diethylaminoethyl acrylate; etc.

As the aromatic vinyl, styrene, α-methylstyrene, vinylpyridine, etc.,may be mentioned.

As the fluorine containing vinyl, fluoroethylvinyl ether,fluoropropylvinyl ether, o-trifluoromethylstyrene, vinylpentafluorobenzoate, difluoroethylene, tetrafluoroethylene, etc., may bementioned.

As the α,β-ethylenically unsaturated monocarboxylic acid, acrylic acid,methacrylic acid, etc., may be mentioned.

As the α,β-ethylenically unsaturated polyvalent carboxylic acid, maleicacid, fumaric acid, itaconic acid, citraconic acid, etc., may bementioned.

As the α,β-ethylenically unsaturated polyvalent carboxylic anhydride,maleic acid anhydride, etc. may be mentioned.

As the copolymerizable anti-aging agent,

-   N-(4-anilinophenyl)acrylamide,-   N-(4-anilinophenyl)methacrylamide,-   N-(4-anilinophenyl)cinnamamide,-   N-(4-anilinophenyl)crotonamide,-   N-phenyl-4-(3-vinylbenzyloxy)aniline,-   N-phenyl-4-(4-vinylbenzyloxy)aniline, etc., may be mentioned.

A plurality of these other copolymerizable monomers may be used incombination. A content of these other monomer units in the nitrilerubber (A1) is preferably 80 wt % or less, more preferably 50 wt % orless and particularly preferably 10 wt % or less, per 100 wt % of thetotal monomer units.

The carboxyl group content in the nitrile rubber (A1) used in the firstaspect, i.e. the number of carboxyl groups (number of moles) included in100 g of the nitrile rubber (A1), is preferably 5×10⁻⁴ to 5×10⁻¹ ephr,more preferably 1×10⁻³ to 1×10⁻¹ ephr and particularly preferably 5×10⁻³to 6×10⁻² ephr. Too small content of carboxyl groups in the nitrilerubber (A1) may result in insufficient cross-link of the crosslinkablerubber composition; and too large content may result in loweringresistance to fatigue of the obtained cross-linked rubber.

The nitrile rubber (A1) has iodine value of 120 or less, preferably 100or less, more preferably 80 or less, further preferably 25 or less andparticularly preferably 15 or less. When the iodine value of the nitrilerubber (A1) is too large, ozone resistance of the obtained cross-linkedrubber may be reduced.

Also, Mooney viscosity [ML₁₊₄ (100° C.)] of the nitrile rubber (A1) ispreferably 15 to 200, more preferably 30 to 150 and particularlypreferably 45 to 120. When the Mooney viscosity of the nitrile rubber(A1) is too low, mechanical strength of the obtained cross-linked rubbermay be reduced; in contrast, too high viscosity may cause to reduceworkability of the obtained crosslinkable rubber composition.

A production method of the above nitrile rubber (A1) is not particularlylimited. Generally, a method to copolymerize α,β-ethylenicallyunsaturated nitrile monomer, α,β-ethylenically unsaturated dicarboxylicacid monoester monomer, diene-based monomer or α-olefin monomer andoptionally-added other monomer copolymerizable with these is convenientand preferable. As a polymerization method, there may be used any knownemulsion polymerization method, suspension polymerization method, bulkpolymerization method and solution polymerization method, and because ofeasy control in polymerization reaction, etc., emulsion polymerizationmethod is preferable.

When iodine value of the copolymer obtained by copolymerization islarger than the above range, hydrogenation of the copolymer(hydrogenation reaction) is recommended. The hydrogenation method is notparticularly limited, and any known method may be employed.

Aromatic Secondary Amine-Based Antioxidant (A2)

The crosslinkable rubber composition according to the first aspectcomprises an aromatic secondary amine-based anti-aging agent (A2) inaddition to the above nitrile rubber (A1).

Although the aromatic secondary amine-based anti-aging agent (A2) is notparticularly limited as far as it is an anti-aging agent having anaromatic secondary amine in its molecule, carbon number is preferably100 or less and particularly preferably 50 or less. As the specificexample, there may be mentioned a diaryl secondary monoamine-basedanti-aging agent such as 4,4′-bis(α,α′-dimethylbenzil)diphenylamine(which may also be referred to as “p,p′-dicumyl diphenylamine”) andoctylated diphenylamine including p,p′-dioctyl diphenylamine, styrenateddiphenylamine and phenyl-α-naphthylamine; a diaryl-p-phenylenediamine-based anti-aging agent such as diphenyl-p-phenylene diamine,mixed diaryl-p-phenylene diamine and dinaphthyl-p-phenylene diamine; andan alkylaryl-p-phenylene diamine-based anti-aging agent such asN-isopropyl-N′-phenyl-p-phenylene diamine,N-1,3-dimethylbutyl-N′-phenyl-p-phenylene diamine,N-(3-methacryloyloxy-2-hydroxypropyl)-N′-phenyl-p-phenylene diamine andN-(methacryloyl)-N′-phenyl-p-phenylene diamine.

A content of the aromatic secondary amine-based anti-aging agent (A2) inthe crosslinkable rubber composition according to the first aspect is,with respect to 100 parts by weight of the nitrile rubber (A1), 0.2 to10 parts by weight, preferably 0.3 to 8 parts by weight and morepreferably 0.5 to 5 parts by weight. When the content of the (A2)component in the crosslinkable rubber composition is too small, it maybe difficult to obtain the effects of the present invention (theinvention according to the first aspect), and in contrast, too largecontent may cause to reduce mechanical strength.

Polyamine-Based Cross-Linking Agent (A3)

The crosslinkable rubber composition according to the first aspectfurther comprises a polyamine-based crosslinking agent (A3) as acrosslinking agent to cross-link the carboxyl groups of the abovenitrile rubber (A1). The polyamine-based crosslinking agent (A3) is notparticularly limited as far as it is (1) a compound having two or moreamino groups, or (2) any one to be in the form of a compound having twoor more amino groups when cross-linking. A compound wherein a pluralityof hydrogens of an aliphatic hydrocarbon or aromatic hydrocarbon issubstituted with an amino group or hydrazide structure (a structureexpressed by “—CONHNH₂” where CO indicates a carbonyl group) ispreferable. As a specific example of polyamine-based crosslinking agent(A3), aliphatic polyvalent amines such as hexamethylene diamine,hexamethylene diamine carbamate, tetramethylene pentamine, hexamethylenediamine cinnamaldehyde adduct and hexamethylene diamine-dibenzoate salt;aromatic polyvalent amines such as2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4′-methylene dianiline,m-phenylene diamine, p-phenylene diamine and 4,4′-methylenebis(o-chloroaniline); a compound having two or more hydrazide structuressuch as isophthalic acid dihydrazide, adipic acid dihydrazide andsebacic acid dihydrazide; may be mentioned. Among these, aliphaticpolyvalent amines are preferable, and hexamethylene diamine carbamate isparticularly preferable.

When using the other crosslinking agent such as a polyvalent epoxycompound, a polyvalent isocyanate compound, an aziridine compound, abasic metal oxide, an organometallic halide, an organic peroxide and thelike instead of the polyamine-based crosslinking agent (A3), it isdifficult to obtain effects of the present invention (the inventionaccording to the first aspect).

A content of the polyamine-based crosslinking agent (A3) in thecrosslinkable rubber composition according to the first aspect is 0.2 to20 parts by weight, preferably 1 to 15 parts by weight and morepreferably 1.5 to 10 parts by weight, with respect to 100 parts byweight of the nitrile rubber (A1). When the content of (A3) component inthe crosslinkable rubber composition is too small, it may be difficultto obtain effects of the present invention (the invention according tothe first aspect); in contrast, too large content may cause reduction inresistance to fatigue.

Other Compounding Agents, Cross-Linking Reaction of Crosslinkable RubberComposition, etc.

In addition to the above nitrile rubber (A1), aromatic secondaryamine-based anti-aging agent (A2) and polyamine-based crosslinking agent(A3), the crosslinkable rubber composition according to the first aspectmay include a compounding agent normally used in the rubber processingfield, e.g. a reinforcement filler such as carbon black and silica, anon-reinforcement filler such as calcium carbonate and clay, ananti-aging agent, a light stabilizer, an antiscorching agent such as aprimary amine, a plasticizer, a processing aid, a lubricant, anadhesive, a lubricating agent, a flame-retardant, a fungicide, anantistatic agent, a coloring agent, a sulfur crosslinking agent, anorganic peroxide crosslinking agent, a crosslinking accelerator,cross-linking auxiliaries, a cross-linking retardant, etc. Amounts ofthe compounding agents are not particularly limited as far as they arein the range not to disturb the purpose and effects of the presentinvention, and those suitable for the purpose of blending can beappropriately selected.

Also, the crosslinkable rubber composition according to the first aspectmay include rubbers other than the nitrile rubber (A1) as far as theamounts are within the range not to disturb the purpose and effects ofthe present invention (the invention according to the first aspect). Thecontent of the rubbers other than the nitrile rubber (A1) in thecrosslinkable rubber composition according to the first aspect ispreferably 30 wt % or less, more preferably 10 wt % or less andparticularly preferably 5 wt % or less.

The crosslinkable rubber composition according to the first aspect isprepared by mixing each of the above components, normally in anonaqueous condition. A method of preparing the crosslinkable rubbercomposition according to the first aspect is not limited, and normally,compounds excluding the crosslinking agent, cross-linking auxiliariesunstable to heat, etc., are primarily kneaded in a mixer such as aBambury mixer, intermixer and kneader, and then secondarily kneadedafter transferring it into a roll, etc. and adding the crosslinkingagent, etc.

For cross-linking the prepared crosslinkable rubber composition toobtain the cross-linked rubber according to the first aspect, theprepared crosslinkable rubber composition is molded by using a moldingmachine suitable for a desired shape, e.g. an extruder, an injectionmolding machine, a compactor, a roll and the like, to fix a shape as across-linked rubber by cross-linking reaction. It may be cross-linkedafter molding or simultaneously. Molding temperature is normally 10 to200° C., preferably 25 to 120° C. Cross-linking temperature is normally100 to 200° C., preferably 130 to 190° C., and cross-linking time isnormally 1 minute to 24 hours, preferably 2 minutes to 1 hour.

Also, depending on the shape, size, etc., of the cross-linked rubber,the inside may not be sufficiently cross-linked even if the surface iscross-linked, so that it may be secondarily cross-linked by furtherheating.

The cross-linked rubber according to the first aspect hascharacteristics that includes well-balanced mechanical strength, such astensile strength and tensile stress, and elongation, and particularlysmall compression set, in addition to intrinsic properties of thenitrile group containing highly-saturated copolymer rubber such asexcellent oil resistance, heat resistance and ozone resistance. Notethat in the first aspect, compression set is preferably 71% or less interms of “O-ring compression set” (a value of O-ring, compression setafter keeping it 25%-compressed at 150° C. for 504 hours) measured in“(8) O-ring set test” of the later-mentioned examples.

Therefore, such a cross-linked rubber according to the first aspect canbe, based on the above properties, used in wide range of applicationincluding those subjected to a strong and repeating shear stress,including a variety of seals such as O-ring, packing, diaphragm,oil-seal, bearing seal and freon seal; a variety of belts such asconveyor belt, V belt, timing belt and synchronous belt; sealrubbercomponents for oilfield such as barb and bubble sheet, BOP (Blow OutPreventer) and platter; attenuation rubber components such as cushioningmaterial and vibration-absorption materials; a variety of hoses such asfuel hose, oil hose, marine hose, riser and flow line, and tubes; and avariety of rolls and roll covers such as printing roll, industrial rolland roll for business equipment; etc., as well as a variety of gasketssuch as intake manifold gasket, locker cover gasket and oil pan gasket;boots; cable coatings; dust cover, automobile interior member, shoesole, etc. It is used preferably for seal, belt, hose, tube, roll cover,gasket, boot and cable coatings, and particularly preferably for seal orbelt.

Particularly, according to the first aspect, such effects, whichmechanical strength, such as tensile strength and tensile stress isexcellently balanced with elongation and compression set is reduced, areadvantageous as the bulk rubber products except for fiber impregnatedbody and metal composite body.

Second Aspect Second Embodiment

Next, a second embodiment, i.e. an embodiment according to the secondaspect the present invention, will be described.

A crosslinkable rubber composition according to the second aspect of thepresent invention comprises 0.1 to 20 parts by weight of a primarymonoamine (B2) having no polar group other than an amino group and 0.1to 20 parts by weight of a polyamine-based crosslinking agent (B3) withrespect to 100 parts by weight of a nitrile rubber (B1) including anα,β-ethylenically unsaturated nitrile monomer unit and anα,β-ethylenically unsaturated dicarboxylic acid monoester monomer unitand having iodine value of 120 or less.

Hereinafter, in the second aspect (second embodiment), the above nitrilerubber (B1) having an α,β-ethylenically unsaturated dicarboxylic acidmonoester monomer unit and iodine value of 120 or less may beabbreviated as “nitrile rubber (B1)”.

Nitrile Rubber (B1)

As the nitrile rubber (B1), the same one as the above-mentioned nitrilerubber (A1) of the first aspect can be used.

Primary Monoamine (B2) Having No Polar Group Other than an Amino Group

The primary monoamine (B2) having no polar group other than an aminogroup [hereinafter it may be simply referred to as “primary monoamine(B2)”.] included in the crosslinkable rubber composition according tothe second aspect is a monoamine compound wherein a hydrocarbon residueand two hydrogen atoms are bound to a nitrogen atom and the hydrocarbonresidue does not have a polar group such as other amino group, iminogroup, hydroxyl group, alkoxy group, carboxyl group, ester group,carbonyl group, formyl group, nitro group, nitrile group, halogen group.When the hydrocarbon residue has two or more amino groups, or a polargroup other than an amino group, it is difficult to obtain effects ofthe present invention (invention according to the second aspect).

The hydrocarbon residue in the primary monoamine (B2) may be eitheraliphatic or aromatic, and aliphatic is preferable. Namely, as theprimary monoamine (B2), an aliphatic primary monoamine is preferable,and more specifically, those having the carbon number of preferably 6 to50, more preferably 8 to 30 and particularly preferably 8 to 20 arepreferable. When carbon number of the hydrocarbon residue of the primarymonoamine (B2) is too small, it may vaporize; in contrast, when it istoo large, mechanical strength of the obtained cross-linked rubber maybe reduced.

Preferable specific examples of the primary monoamine (B2) may includenonadecylamine, octadecylamine, hexadecylamine, tridecylamine,decylamine and octylamine, and octadecylamine is particularlypreferable.

A content of the primary monoamine (B2) in the crosslinkable rubbercomposition according to the second aspect is 0.1 to 20 parts by weight,preferably 0.2 to 5 parts by weight and more preferably 0.3 to 2 partsby weight with respect to 100 parts by weight of the nitrile rubber(B1). When the content of the primary monoamine (B2) component is toosmall in the crosslinkable rubber composition, workability and scorchstability may be deteriorated; in contrast, too large content may causeto reduce mechanical strength of the obtained cross-linked rubber.

Polyamine-Based Cross-Linking Agent (B3)

As the polyamine-based crosslinking agent (B3), the crosslinking agentsame as the above-mentioned polyamine-based crosslinking agent (A3) ofthe first aspect can be used.

In the second aspect, a content of the polyamine-based crosslinkingagent (B3) is 0.1 to 20 parts by weight, preferably 0.3 to 15 parts byweight and more preferably 0.5 to 10 parts by weight with respect to 100parts by weight of the nitrile rubber (B1). When the content of the (B3)component is too small in the crosslinkable rubber composition,compression set tends to increase in the obtained cross-linked rubber.On the other hand, too large content may cause reduction in resistanceto fatigue of the obtained cross-linked rubber.

Other Compounding Agent, Cross-Linking Reaction of Crosslinkable RubberComposition, etc.

The crosslinkable rubber composition according to the second aspect mayarbitrarily include a compounding agent normally used in the rubberprocessing field in addition to the above nitrile rubber (B1), primarymonoamine (B2) and polyamine-based crosslinking agent (B3). As thecompounding agent, those same as in the above-mentioned first aspect canbe used. Similarly, the crosslinkable rubber composition according tothe second aspect may include rubbers other than the nitrile rubber (B1)as far as not disturbing purpose and effects of the present invention.The amounts may be same as in the above-mentioned first aspect.

The crosslinkable rubber composition according to the second aspect isprepared, as with the above-mentioned first aspect, by mixing each ofthe above components in a nonaqueous condition. Then, the preparedcrosslinkable rubber composition is molded, cross-linked, andsecondarily cross-linked if needed to obtain the cross-linked rubberaccording to the second aspect.

The cross-linked rubber according to the second aspect shows sufficientmechanical strength, such as tensile strength and tensile stress, andelongation, and particularly small compression set, in addition to theintrinsic properties of the nitrile group containing highly-saturatedcopolymer rubber such as excellent oil resistance, heat resistance andozone resistance. Note that in the second aspect, compression set ispreferably 70% or less, more preferably 60% or less, in terms of “O-ringcompression set” (a value of O-ring compression set after keeping it25%-compressed at 150° C. for 168 hours) measured in “(11) O-ring settest” of the later-mentioned examples.

Therefore, such a cross-linked rubber according to the second aspect canbe, based on the above properties, preferably used in variousapplications, for example, in the same applications as in theabove-mentioned first aspect.

Particularly, according to the second aspect, such effects, whichmechanical strength, such as tensile strength and tensile stress, andelongation are sufficient, and compression set is reduced, areadvantageous as the bulk rubber products except for fiber impregnatedbody and metal composite body.

Third Aspect Third Embodiment

Next, a third embodiment, i.e. an embodiment according to the thirdaspect of the present invention, will be described.

A crosslinkable rubber composition according to the third aspect of thepresent invention comprises a nitrile group containing highly-saturatedcopolymer rubber (C1), a polyoxyalkylene alkyl ether phosphate ester(C2) and a polyamine-based crosslinking agent (C3).

Hereinafter, in the third aspect (third embodiment), the above nitrilegroup containing highly-saturated copolymer rubber (C1) may beabbreviated as “highly-saturated nitrile rubber (C1)”.

Highly-Saturated Nitrile Rubber (C1)

A preferable mode to form a nitrile group of the highly-saturatednitrile rubber (C1) is the one in which the rubber has anα,β-ethylenically unsaturated nitrile monomer unit.

As a monomer forming the α,β-ethylenically unsaturated nitrile monomerunit, although not limited as far as it is an α,β-ethylenicallyunsaturated compound having a nitrile group, for example, same monomersas in above-mentioned nitrile rubber (A1) of the first aspect can beused. Also, the content of the α,β-ethylenically unsaturated nitrilemonomer unit may be same as in the above-mentioned first aspect.

In the highly-saturated nitrile rubber (C1), a diene-based monomer unitor α-olefin monomer unit is normally included so that the cross-linkedrubber has rubber elasticity.

As a diene-based monomer and α-olefin monomer forming the diene-basedmonomer unit and α-olefin monomer unit, same monomers can be used as inthe above-mentioned nitrile rubber (A1) of the first aspect. Also, thecontents of these monomer units may be same as in the above-mentionedfirst aspect.

The highly-saturated nitrile rubber (C1) preferably contains a carboxylgroup. When the highly-saturated nitrile rubber (C1) contains a carboxylgroup, the obtained cross-linked rubber tends to improve tensilestrength.

As a mode to contain a carboxyl group in the highly-saturated nitrilerubber (C1), the one in which molecular structure of the rubber has anα,β-ethylenically unsaturated carboxylic acid monomer unit, anα,β-ethylenically unsaturated dicarboxylic acid monoester monomer unitor an α,β-ethylenically unsaturated dicarboxylic acid monomer unit ispreferable, and the one having an α,β-ethylenically unsaturateddicarboxylic acid monoester monomer unit is more preferable.

As a preferable method to contain an α,β-ethylenically unsaturateddicarboxylic acid monoester monomer unit in the highly-saturated nitrilerubber (C1) which is the above-mentioned more preferable mode, there maybe mentioned a method to copolymerize an α,β-ethylenically unsaturateddicarboxylic acid monoester monomer with the above α,β-ethylenicallyunsaturated nitrile monomer.

As an organic group, binding to a carbonyl group through an oxygen atom,in an ester structure of the α,β-ethylenically unsaturated dicarboxylicacid monoester monomer, an alkyl group, a cycloalkyl group and analkylcycloalkyl group may be mentioned, and among these, alkyl group ispreferable. Carbon number of the alkyl group, consequently an alkoxygroup, is preferably 3 to 8, more preferably 4 to 6. When carbon numberis too small, processing stability of the crosslinkable rubbercomposition may be reduced; in contrast, too large carbon number maycause slowed cross-linking rate and lowered mechanical strength of theobtained cross-linked rubber.

As the above α,β-ethylenically unsaturated dicarboxylic acid monoestermonomer, for example, same monomers as in the above-mentioned nitrilerubber (A1) of the first aspect can be used. Also, the content of theα,β-ethylenically unsaturated dicarboxylic acid monoester monomer unitmay be same as in the above-mentioned first aspect.

The highly-saturated nitrile rubber (C1) may include other monomer unitcopolymerizable with a monomer forming each of the above monomer units,i.e. the α,β-ethylenically unsaturated nitrile monomer, diene-basedmonomer or α-olefin monomer, and α,β-ethylenically unsaturateddicarboxylic acid monoester monomer. As the other monomer, for example,same monomers as in the above-mentioned nitrile rubber (A1) of the firstaspect can be used. Also, the content of the other copolymerizablemonomer unit may be same as in the above-mentioned first aspect.

It is preferable that the carboxy group content, iodine value and Mooneyviscosity [ML₁₊₄ (100° C.)] of the highly-saturated nitrile rubber (C1)are within the same ranges as in the above-mentioned nitrile rubber (A1)of the first aspect. Also, highly-saturated nitrile rubber (C1) may beproduced as with the above-mentioned nitrile rubber (A1) of the firstaspect.

Polyoxyalkylene Alkyl Ether Phosphate Ester (C2)

The crosslinkable rubber composition according to the third aspectcomprises a polyoxyalkylene alkyl ether phosphate ester (C2) in additionto the above-mentioned highly-saturated nitrile rubber (C1). Thepolyoxyalkylene alkyl ether phosphate ester (C2) is a phosphatemonoester, diester or triester, containing a polyoxyalkylene alkyl ethergroup, and may be a mixture of these.

Among these, from viewpoint of improvement in heat aging resistance andreduction in compression set, the monoester having a chemical structureexpressed by the following formula (1) is preferable.

In this formula, R₁ is an alkyl group with carbon number of 1 to 30;each of R₂ and R₃ is independently a hydrogen or alkyl group with carbonnumber of 1 to 10; q is the number of moles of an added alkylene oxideand a natural number of 2 to 50; r is the number of the polyoxyalkylenealkyl ether group which is 1, 2 or 3. In the above formula, q and r areindependently selected from the above ranges.

The polyoxyalkylene alkyl ether phosphate ester (C2) of the aboveformula (1) is those having alkyl group R₁ with carbon number ofpreferably 8 to 22, more preferably 10 to 20. Also preferably, each ofR₂ and R₃ is independently a hydrogen or alkyl group with carbon numberof 1 to 3, and more preferably a hydrogen or methyl group, and it isparticularly preferable that both are hydrogen groups. The number ofmoles, q, of an added alkylene oxide is preferably 8 to 30, morepreferably 10 to 20.

The content of the polyoxyalkylene alkyl ether phosphate ester (C2) inthe crosslinkable rubber composition according to the third aspect ispreferably 0.05 to 20 parts by weight, more preferably 0.1 to 10 partsby weight and particularly preferably 0.3 to 5 parts by weight withrespect to 100 parts by weight of the highly-saturated nitrile rubber(C1). By making the content within the above range, effects ofimprovement in heat aging resistance and reduction in compression setare further significant.

Polyamine-Based Cross-Linking Agent (C3)

It is preferable that the crosslinkable rubber composition according tothe third aspect includes a polyamine-based crosslinking agent (C3) as acrosslinking agent for forming a cross-linked rubber.

As the polyamine-based crosslinking agent (C3), same crosslinking agentsas in the above-mentioned polyamine-based crosslinking agent (A3) of thefirst aspect can be used. Also, the content of the polyamine-basedcrosslinking agent (C3) is preferably 0.1 to 20 parts by weight, morepreferably 0.2 to 15 parts by weight and particularly preferably 0.3 to10 parts by weight with respect to 100 parts by weight of thehighly-saturated nitrile rubber (C1). When the content of thepolyamine-based crosslinking agent (C3) is too small, the obtainedcross-linked rubber may be insufficient in cross-link, resulting inreduction in mechanical strength or increase in compression set; incontrast, too large content may cause reduction in elongation.

Note that in the third aspect, it is preferable to use thepolyamine-based crosslinking agent (C3) as a crosslinking agent, butinstead of the polyamine-based crosslinking agent (C3), there may beused another crosslinking agent such as an organic peroxide, asulfur-based crosslinking agent, a resin crosslinking agent, apolyvalent epoxy compound, a polyvalent isocyanate compound, apolyvalent alcohol compound, an aziridine compound, a basic metal oxideand an organometallic halide.

As the organic peroxide, dialkyl peroxides, diacyl peroxides,peroxyesters may be mentioned.

As the dialkyl peroxides, there may be mentioned dicumyl peroxide,di-t-butylperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexine,2,5-dimethyl-2,5-di(t-butylperoxy)hexane,1,3-bis(t-butylperoxyisopropyl)benzene, etc. As the diacyl peroxides,there may be mentioned benzoyl peroxide, isobutyryl peroxide, etc. Asthe peroxyesters, there may be mentioned2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, t-butylperoxyisopropylcarbonate, etc.

As the sulfur-based crosslinking agent, there may be mentioned a sulfursuch as powdered sulfur and precipitated sulfur; and an organic sulfurcompound such as 4,4′-dithiomorpholine, tetramethylthiuram disulfide,tetraethylthiuram disulfide and polymer polysulfide.

As the resin crosslinking agent, there may be mentionedalkylphenol-formaldehyde resin, melamine-formaldehyde condensate,triazine-formaldehyde condensate, octylphenol-formaldehyde resin,alkylphenol-sulfide resin, hexamethoxymethyl-melamine resin.

As the polyvalent epoxy compound, there may be mentioned a compoundhaving two or more epoxy groups in a molecule, including a glycidylether-type epoxy compound such as a phenol novolac-type epoxy compound,a cresol novolac-type epoxy compound, a cresol-type epoxy compound, abisphenol A type epoxy compound, a bisphenol F type epoxy compound, abrominated bisphenol A type epoxy compound, a brominated bisphenol Ftype epoxy compound and a hydrogenated bisphenol A type epoxy compound;a polyvalent epoxy compound such as an alicyclic epoxy compound, aglycidyl ester-type epoxy compound, a glycidyl amine-type epoxy compoundand an isocyanurate-type epoxy compound; etc. These can be used alone orin combination of two or more.

As the polyvalent isocyanate compound, diisocyanates and triisocyanates,with carbon number 6 to 24, are preferable.

As a specific example of the diisocyanates, there may be mentioned2,4-tolylenediisocyanate (2,4-TDI), 2,6-tolylenediisocyanate (2,6-TDI),4,4′-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate,p-phenylene diisocyanate, m-phenylene diisocyanate, 1,5-naphthylenediisocyanate, etc. Also, as a specific example of triisocyanates, theremay be mentioned 1,3,6-hexamethylene triisocyanate, 1,6,11-undecanetriisocyanate, bicycloheptane triisocyanate, etc. These can be usedalone or in combination of two or more.

As the polyvalent alcohol compound, there may be mentioned alow-molecular-weight polyol such as ethylene glycol, propylene glycol,butylene glycol, hexamethylene glycol, diethylene glycol, dipropyleneglycol, triethylene glycol, polyethylene glycol, polyoxypropyleneglycol, 1,7-heptanediol, 1,8-octanediol, hydrobenzoin, benzpinacol,cyclohexanedimethanol, glycerin, trimethylolethane, trimethylolpropane,pentaerythritol, dipentaerythritol, trimethylolethane, trimethylolhexaneand bisphenol A; a polyol wherein an alkylene oxide is additivelypolymerized to a low-molecular-weight polyol such as diethylene glycol,dipropylene glycol, butanediol and glycerin; a polyol wherein analkylene oxide is additively polymerized to a low-molecular-weight aminesuch as triethanolamine, ethylamine, propylamine, ethylenediamine,triethylenediamine and diethylenetriamine; a polysaccharides such asarbitol, sorbitol, sorbitan, xylose, arabinose, glucose, galactose,sorbose, fructose and sorbitan propylester; a polymer having a pluralityof hydroxyl groups in a molecule such as polyglycerin ester, polyvinylalcohol, a polyolefin-based oligomer having a plurality of hydroxylgroups and ethylene-hydroxyethyl(meth)acrylate copolymer; a cycliccompound having a plurality of hydroxyl groups such as a spiroglycolhaving a hydroxyl group terminally, a dioxane glycol having a hydroxylgroup terminally, a tricyclodecane-dimethanol having a hydroxyl groupterminally and a macromonomer having a hydroxyl group terminally and apolystyrene side-chain; etc. These can be used alone or in combinationof two or more.

As the aziridine compound, there may be mentionedtris-2,4,6-(1-aziridinyl)-1,3,5-triazine,tris[1-(2-methyl)aziridinyl]phosphinoxide,hexa[1-(2-methyl)aziridinyl]triphosphatriazine, etc. These can be usedalone or in combination of two or more.

As the basic metal oxide, there may be mentioned zinc oxide, lead oxide,calcium oxide, magnesium oxide, etc. These can be used alone or incombination of two or more.

As the organometallic halide, dicyclopentadienyl metal dihalide may beexemplified. The metal may include titanium, zirconium, hafnium, etc.

When using these crosslinking agents other than the polyamine-basedcrosslinking agent (C3), the content in the crosslinkable rubbercomposition may be same as in the case of using the polyamine-basedcrosslinking agent (C3).

Other Compounding Agent, Cross-Linking Reaction of Crosslinkable RubberComposition, etc.

The crosslinkable rubber composition according to the third aspect mayarbitrarily include a compounding agent normally used in the rubberprocessing field in addition to each of the above-mentioned components.As the compounding agent, those same as in the above-mentioned firstaspect can be used. Similarly, the crosslinkable rubber compositionaccording to the third aspect may include rubbers other than thehighly-saturated nitrile rubber (C1) as far as not disturbing purposeand effects of the present invention. The amounts may be same as in theabove-mentioned first aspect.

The crosslinkable rubber composition according to the third aspect isprepared, as with the above-mentioned first aspect, by mixing each ofthe above components in a nonaqueous condition. Then, the preparedcrosslinkable rubber composition is molded, cross-linked, andsecondarily cross-linked if needed to obtain the cross-linked rubberaccording to the third aspect.

The cross-linked rubber according to the third aspect shows excellentheat aging resistance and significantly small compression set, inaddition to the intrinsic properties of the nitrile group containinghighly-saturated copolymer rubber such as excellent oil resistance andozone resistance.

Therefore, such a cross-linked rubber according to the third aspect canbe, based on the above properties, preferably used in variousapplications, for example, in the same applications as in theabove-mentioned first aspect.

Particularly, according to the third aspect, such effects, whichmechanical strength, such as tensile strength and tensile stress, isexcellent and compression set is reduced, are advantageous as the bulkrubber products except for fiber impregnated body and metal compositebody.

Fourth Aspect Fourth Embodiment

Next, a fourth embodiment, i.e. an embodiment according to the fourthaspect of the present invention, will be described.

A crosslinkable rubber composition according to the fourth aspect of thepresent invention comprises, with respect to a total of 100 parts byweight of a nitrile group containing highly-saturated copolymer rubber(D1) having an α,β-ethylenically unsaturated dicarboxylic acid monoestermonomer unit and an acrylic rubber (D2) having an α,β-ethylenicallyunsaturated dicarboxylic acid monoester monomer unit, 0.2 to 20 parts byweight of a polyamine-based crosslinking agent (D3).

Hereinafter, in the fourth aspect (fourth embodiment), the above nitrilegroup containing highly-saturated copolymer rubber (D1) and acrylicrubber (D2) having an α,β-ethylenically unsaturated dicarboxylic acidmonoester monomer unit may be abbreviated as “nitrile rubber (D1)” and“acrylic rubber (D2)”, respectively.

Nitrile Rubber (D1)

A preferable mode to form a nitrile group of the nitrile rubber (D1) isthe one in which the rubber has an α,β-ethylenically unsaturated nitrilemonomer unit.

As a monomer forming the α,β-ethylenically unsaturated nitrile monomerunit, although not limited as far as it is an α,β-ethylenicallyunsaturated compound having a nitrile group, for example, same monomersas in above-mentioned nitrile rubber (A1) of the first aspect can beused. Also, the content of the α,β-ethylenically unsaturated nitrilemonomer unit may be same as in the above-mentioned first aspect.

The nitrile rubber (D1) comprises an α,β-ethylenically unsaturateddicarboxylic acid monoester monomer unit in addition to theα,β-ethylenically unsaturated nitrile monomer unit. When the nitrilerubber (D1) contains an α,β-ethylenically unsaturated dicarboxylic acidmonoester monomer unit, the obtained cross-linked rubber tends toimprove tensile strength.

As a preferable method to contain an α,β-ethylenically unsaturateddicarboxylic acid monoester monomer unit in the nitrile rubber (D1),there may be mentioned a method to copolymerize an α,β-ethylenicallyunsaturated dicarboxylic acid monoester monomer with the aboveα,β-ethylenically unsaturated nitrile monomer.

As an organic group, binding to a carbonyl group through an oxygen atom,in an ester structure of the α,β-ethylenically unsaturated dicarboxylicacid monoester monomer, an alkyl group, cycloalkyl group andalkylcycloalkyl group are mentioned, and the alkyl group is preferableamong these. Carbon number of the alkyl group, consequently an alkoxygroup, is preferably 3 to 8, more preferably 4 to 6. When carbon numberis too small, processing stability of the crosslinkable rubbercomposition may be reduced; in contrast, too large carbon number maycause slowed cross-linking rate and lowered mechanical strength of theobtained cross-linked rubber.

As the above α,β-ethylenically unsaturated dicarboxylic acid monoestermonomer, for example, same monomers as in the above-mentioned nitrilerubber (A1) of the first aspect can be used. Also, the content of theα,β-ethylenically unsaturated dicarboxylic acid monoester monomer unitmay be same as in the above-mentioned first aspect.

The nitrile rubber (D1) normally comprises a diene-based monomer unitand/or α-olefin monomer unit to allow the cross-linked rubber havingrubber elasticity.

As a diene-based monomer and α-olefin monomer forming the diene-basedmonomer unit and α-olefin monomer unit respectively, same monomers canbe used as in the above-mentioned nitrile rubber (A1) of the firstaspect. Also, the contents of these monomer units may be same as in theabove-mentioned first aspect.

The nitrile rubber (D1) may comprise other monomer units copolymerizablewith the monomer forming each of the above monomer unit, i.e.α,β-ethylenically unsaturated nitrile monomer, α,β-ethylenicallyunsaturated dicarboxylic acid monoester monomer, and diene-based monomeror α-olefin monomer. As other monomers, for example, same monomers canbe used as in the above-mentioned nitrile rubber (A1) of the firstaspect. Also, the content of the other copolymerizable monomer unit maybe same as in the above-mentioned first aspect.

It is preferable that the carboxyl group content, iodine value andMooney viscosity [ML₁₊₄ (100° C.)] of the nitrile rubber (D1) are withinthe same ranges as in the above-mentioned nitrile rubber (A1) of thefirst aspect. Also, the nitrile rubber (D1) may be produced as with theabove-mentioned nitrile rubber (A1) of the first aspect.

Acrylic Rubber (D2)

The acrylic rubber (D2) having an α,β-ethylenically unsaturateddicarboxylic acid monoester monomer unit used in the fourth aspect is arubber containing an acrylic acid ester monomer unit which is a maincomponent unit and an α,β-ethylenically unsaturated dicarboxylic acidmonoester monomer unit.

A total amount of the acrylic acid ester monomer unit andα,β-ethylenically unsaturated dicarboxylic acid monoester monomer unitin the acrylic rubber (D2) is preferably 70 wt % or more, morepreferably 80 wt % or more and particularly preferably 90 wt % or more,per 100 wt % of all monomer units.

Also, when the total amount of the acrylic acid ester monomer unit andα,β-ethylenically unsaturated dicarboxylic acid monoester monomer unitin the acrylic rubber (D2) is defined as 100 wt %, a ratio of theacrylic acid ester monomer unit is preferably 90 to 99.5 wt %, morepreferably 95 to 99 wt %.

On the other hand, in the acrylic rubber (D2), when the total amount ofthe acrylic acid ester monomer unit and α,β-ethylenically unsaturateddicarboxylic acid monoester monomer unit is defined as 100 wt %, a ratioof the α,β-ethylenically unsaturated dicarboxylic acid monoester monomerunit is preferably 0.5 to 10 wt %, more preferably 1 to 5 wt %.

When the ratio of the acrylic acid ester monomer unit is too large, theeffects of the present invention (the invention according to the fourthaspect) may not be obtained; in contrast, when the ratio of the acrylicacid ester monomer unit is too small, mechanical strength and elongationof the obtained cross-linked rubber may be reduced.

The carboxyl group content of the acrylic rubber (D2) used in the fourthaspect, i.e. the number of carboxyl groups (number of moles) per 100 gof the acrylic rubber (D2), is preferably 5×10⁻⁴ to 5×10⁻¹ ephr, morepreferably 1×10⁻³ to 1×10⁻¹ ephr and particularly preferably 5×10⁻³ to6×10⁻² ephr. When the carboxyl group content of the acrylic rubber (D2)is too small, mechanical strength of the obtained cross-linked rubbermay be reduced; in contrast, when it is too large, remaining carboxylgroups after cross-link may result in deterioration in resistance tofatigue of the obtained cross-linked rubber.

In the fourth aspect, the acrylic rubber (D2) is preferably:

(i) an acrylic rubber consisting of an acrylic acid alkyl ester monomerunit having an alkyl group with carbon number of 1 to 8 as the maincomponent unit; or

(ii) an acrylic rubber wherein an acrylic acid alkyl ester monomer unithaving an alkyl group with carbon number of 1 to 8 and an acrylic acidalkoxyalkyl ester monomer unit having a sum of carbon numbers of analkyl group and alkoxy group of 1 to 8 are used in combination as themain component unit.

As a monomer forming the above acrylic acid alkyl ester monomer unithaving an alkyl group with carbon number of 1 to 8, an acrylic acidalkyl ester monomer having an alkyl group with carbon number of 1 to 4is preferable, and for example, methyl acrylate, ethyl acrylate, propylacrylate, n-butyl acrylate, etc., may be mentioned.

As a monomer forming the above acrylic acid alkoxyalkyl ester monomerunit having a sum of carbon numbers of an alkyl group and alkoxy groupof 1 to 8, an acrylic acid alkoxyalkyl ester monomer having an alkylgroup with carbon number of 1 to 4 and an alkoxy group with carbonnumber of 1 to 4 is preferable, and for example, methoxymethyl acrylate,methoxyethyl acrylate, ethoxyethyl acrylate, butoxyethyl acrylate, etc.,may be mentioned.

As a monomer forming the α,β-ethylenically unsaturated dicarboxylic acidmonoester monomer unit constituting the acrylic rubber (D2), theα,β-ethylenically unsaturated dicarboxylic acid monoester monomer usedas a monomer forming the above-mentioned nitrile rubber (D1) may be usedas well.

The acrylic rubber (D2) may contain, in addition to the acrylic acidester monomer unit which is the main component unit andα,β-ethylenically unsaturated dicarboxylic acid monoester monomer unit,a crosslinkable monomer unit copolymerizable with these in a ratio ofpreferably 10 wt % or less, more preferably 5 wt % or less, per 100 wt %of all monomer units.

As the crosslinkable monomer, for example, an active chlorine groupcontaining unsaturated monomer, an epoxy group containing monomer, acarboxyl group containing monomer, a diene-based monomer, etc., may bementioned.

As the active chlorine group containing unsaturated monomer, there maybe mentioned vinyl chloroacetate, vinylbenzyl chloride, allylchloroacetate, vinyl chlorobutyrate, 2-chloroethyl acrylate,3-chloropropyl acrylate, 4-chlorobutyl acrylate, 2-chloroethylmethacrylate, 2-chloroethyl vinyl ether, chloromethyl butenyl ketone,1-chloro-2-butenyl acrylate, 5-chloromethyl-2-norbornene,5-chloroacetoxymethyl-2-norbornene and5-(α,β-dichloropropionylmethyl)-2-norbornene.

As the epoxy group containing monomer, there may be mentioned anunsaturated glycidyl ester such as glycidyl acrylate, glycidylmethacrylate, diglycidyl itaconate, butene tricarboxylic acidtriglycidyl and p-styrene carboxylic acid glycidyl; an unsaturatedglycidyl ether such as vinylglycidyl ether, allylglycidyl ether andmethacryl glycidyl ether; etc.

As the carboxyl group containing monomer, there may be mentionedunsaturated carboxylic acid monomer other than α,β-ethylenicallyunsaturated dicarboxylic acid monoester monomer, such as acrylic acid,methacrylic acid, itaconic acid, maleic acid, fumaric acid,2-norbornene-5-carboxylic acid and maleic anhydride.

As the diene-based monomer, the diene-based monomer for forming theabove-mentioned nitrile rubber (D1) may be used as well.

The acrylic rubber (D2) may further contain, in addition to the acrylicacid ester monomer, the α,β-ethylenically unsaturated dicarboxylic acidmonoester monomer and the crosslinkable monomer, other monomer unitscopolymerizable with these as far as not disturbing effects of thepresent invention. As the other monomers, an ethylenically unsaturatedmonomer, not including the above acrylic acid ester monomer,α,β-ethylenically unsaturated dicarboxylic acid monoester monomer andcrosslinkable monomer, may be exemplified.

Specific examples of such an ethylenically unsaturated monomer includeethylene, acrylonitrile, vinyl acetate, styrene, α-methylstyrene,acrylamide, polyalkylene glycol acrylic acid ester, methacrylonitrile,etc. The content of the other monomer unit in the acrylic rubber (D2) ispreferably 50 wt % or less, more preferably 40 wt % or less, furtherpreferably 30 wt % or less and particularly preferably 10 wt % or lessper 100 wt % of all monomer units.

Mooney viscosity [ML₁₊₄ (100° C.)] of the acrylic rubber (D2) ispreferably 10 to 100, more preferably 15 to 80 and particularlypreferably 20 to 60. When Mooney viscosity of the acrylic rubber (D2) istoo low, strength property of the obtained cross-linked rubber may bereduced; in contrast, too high Mooney viscosity may cause reduction inworkability of the crosslinkable rubber composition.

A production method of the acrylic rubber (D2) is not limited, and anygeneral production method for an acrylic rubber may be applicable. Forexample, each of the above monomers can be copolymerized by usingpolymerization procedure such as emulsion polymerization, suspensionpolymerization, solution polymerization and bulk polymerization using aradical initiator including persulfate such as potassium persulfate andammonium persulfate; organic peroxide such as cumene hydroperoxide;etc., to produce the acrylic rubber (D2). Batch polymerization may beapplicable, or polymerization may be done by either continuously orintermittently adding one or more monomer components during it.Polymerization temperature is preferably 0 to 100° C., more preferably 2to 80° C.

In the fourth aspect, weight ratio of the nitrile rubber (D1) and theacrylic rubber (D2) in the crosslinkable rubber composition ispreferably 5/95 to 95/5, more preferably 10/90 to 90/10, furtherpreferably 20/80 to 80/20 and particularly preferably 30/70 to 70/30.When the ratio of the acrylic rubber (D2) is too small, heat resistanceof the obtained cross-linked rubber may be insufficient, and compressionset of the cross-linked rubber (particularly a cross-linked article withspace portion) may not be sufficiently small. In contrast, when it istoo large, mechanical strength of the obtained cross-linked rubber maybe reduced.

Polyamine-Based Cross-Linking Agent (D3)

As the polyamine-based crosslinking agent (D3), same crosslinking agentsas in the above-mentioned polyamine-based crosslinking agent (A3) of thefirst aspect can be used.

In the fourth aspect, the content of the polyamine-based crosslinkingagent (D3) is 0.2 to 20 parts by weight, preferably 0.5 to 15 parts byweight and more preferably 1 to 10 parts by weight with respect to atotal of 100 parts by weight of the nitrile rubber (D1) and acrylicrubber (D2). When the content of the (D3) component in the crosslinkablerubber composition is too small, effects of the present invention (theinvention according to the fourth aspect) may not be fully obtained. Incontrast, when it is too large, storage stability of the crosslinkablerubber composition may be reduced, and the obtained cross-linked rubbermay be brittle due to too high crosslink density.

Basic Cross-Linking Accelerator (D4)

It is preferable that the crosslinkable rubber composition according tothe fourth aspect further contains the basic crosslinking accelerator(D4). As the basic crosslinking accelerator (D4), there may be mentioneda guanidine-based crosslinking accelerator such as tetramethylguanidine,tetraethylguanidine, diphenylguanidine, di-o-tolylguanidine,o-tolylbiguanide and di-o-tolylguanidine salt of dicatechol borate; analdehydeamine-based crosslinking accelerator such as n-butylaldehydeaniline and acetaldehyde ammonia; etc. Among these, the guanidine-basedcrosslinking accelerator is preferable.

The amount of the basic crosslinking accelerator (D4) is preferably 0.5to 10 parts by weight, more preferably 1 to 7.5 parts by weight andparticularly preferably 1.5 to 5 parts by weight with respect to a totalof 100 parts by weight of the nitrile rubber (D1) and acrylic rubber(D2). When the amount of the basic crosslinking accelerator (D4) is toosmall, cross-linking rate of the crosslinkable rubber composition may beslowed and crosslink density may be reduced. In contrast, when it is toolarge, too high cross-linking rate may cause scorch, resulting indeterioration in storage stability.

Other Compounding Agent, Cross-Linking Reaction of Crosslinkable RubberComposition, etc.

The crosslinkable rubber composition according to the fourth aspect mayarbitrarily include a compounding agent normally used in the rubberprocessing field in addition to each of the above components. As thecompounding agent, those same as in the above-mentioned first aspect[note that the one corresponding to the above (D4) component isexcluded] may be used. Similarly, the crosslinkable rubber compositionaccording to the fourth aspect may include rubbers other than thenitrile rubber (D1) and acrylic rubber (D2) as far as not disturbing thepurpose and effects of the present invention. The amounts may be same asin the above-mentioned first aspect.

The crosslinkable rubber composition according to the fourth aspect isprepared, as with the above-mentioned first aspect, by mixing each ofthe above components in a nonaqueous condition. Then, the preparedcrosslinkable rubber composition is molded, cross-linked, andsecondarily cross-linked if needed to obtain the cross-linked rubberaccording to the fourth aspect.

The cross-linked rubber according to the fourth aspect showssignificantly small compression set as well as excellent mechanicalstrength and heat resistance. Note that compression set of thecross-linked rubber according to the fourth aspect is preferably 40% orless, more preferably 35% or less, in terms of “O-ring compression set”(a value of O-ring compression set after keeping it 25%-compressed at150° C. for 168 hours) measured in “(11) O-ring set test” of thelater-mentioned examples.

Therefore, such a cross-linked rubber according to the fourth aspect canbe, based on the above properties, preferably used in variousapplications, for example, in the same applications as in theabove-mentioned first aspect.

Particularly, according to the fourth aspect, when using it as sealmaterial, such effects, which mechanical strength and heat resistanceare excellent as well as significantly small compression set, areremarkable.

Examples

Hereinafter, the present invention will be specifically described basedon production examples, inventive examples and comparative examples, butthe present invention is not limited to these examples. Note that“parts” in the following description indicates a weight base unlessotherwise designated.

Examples and Comparative Examples According to the First Aspect

First, production examples (production examples 1-1 and 1-2), examples(examples 1-1 to 1-5) according to the first aspect and comparativeexamples (comparative examples 1-1 to 1-7) will be described. Note thatin the examples and comparative examples according to the first aspect,each of the following tests (1) to (8) and evaluation.

(1) Content of Carboxyl Groups

The content of carboxyl groups in the nitrile rubber was determined asthe number of carboxyl groups (number of moles, unit is ephr) per 100 gof the rubber by titration at room temperature using a hydrous ethanolsolution (0.02 N) of potassium hydroxide and thymolphtalein as anindicator.

(2) Iodine Value

Iodine value was measured according to JIS K6235.

(3) Mooney Viscosity [ML₁₊₄ (100° C.)]

Mooney viscosities of the nitrile rubber (polymer Mooney) and thecrosslinkable rubber composition (compound Mooney) were measuredaccording to JIS K6300.

(4) Normal Physical Property (Tensile Strength and Elongation)

The crosslinkable rubber composition was cross-linked at 170° C. for 20minutes at a pressure of 10 MPa to prepare a pressed cross-linked testspecimen. Tensile strength and elongation of the cross-linked rubberwere measured according to JIS K6251 by using this pressed cross-linkedtest specimen.

(5) Normal Physical Property (100% Tensile Stress)

100% tensile stress of the cross-linked rubber was measured according toJIS K6251 under the same conditions as above (4).

(6) Normal Physical Property (Tensile Strength and Elongation) AfterSecondary Cross-Link

The crosslinkable rubber composition was cross-linked at 170° C. for 20minutes at a pressure of 10 MPa, followed by secondary cross-link in ageared oven at 170° C. for 4 hours, to prepare a test specimen. Tensilestrength, 100% tensile stress and elongation of the cross-linked rubberafter secondary cross-link were measured according to JIS K6251 by usingthis test specimen.

(7) Normal Physical Property (100% Tensile Stress) After SecondaryCross-Link

100% tensile stress of the cross-linked rubber after secondarycross-link was measured according to JIS K6251 under the same conditionsas above (6).

(8) O-Ring Set Test (150° C., 504 Hours)

By using a mold with an internal diameter of 30 mm and a ring diameterof 3 mm, the crosslinkable rubber composition was cross-linked at 170°C. for 20 minutes at a pressure of 10 MPa, followed by secondarycross-link at 170° C. for 4 hours, to obtain a test specimen for O-ringset test. Then, O-ring compression set was measured according to JISK6262 under a condition of compressing a distance of two planessandwiching an O-ring by 25% in a ring thickness direction at 150° C.for 504 hours.

Production Example 1-1

180 parts of ion-exchanged water, 25 parts of sodiumdodecylbenzenesulfonate (emulsifier) solution in a concentration of 10wt %, 37 parts of acrylonitrile, 8 parts of mono-n-butyl fumarate and0.5 part of t-dodecylmercaptan (molecular weight modifier) was placed insequence into a metallic bottle. After replacing the gas in the bottlewith nitrogen three times, 55 parts of 1,3-butadiene was added. 0.1 partof Cumene hydroperoxide (polymerization catalyst) was added to themetallic bottle kept at 5° C., followed by polymerization reaction for16 hours while rotating the metallic bottle. Then, after 0.1 part ofhydroquinone (polymerization terminator) solution in a concentration of10 wt % was added to terminate the polymerization reaction, remainingmonomers were removed by using a rotary evaporator with watertemperature of 60° C. to obtain a latex (solid content concentration ofabout 30 wt %) of an acrylonitrile-butadiene-α,β-ethylenicallyunsaturated dicarboxylic acid monoalkyl ester copolymer rubbercomprising 34 wt % of acrylonitrile units, 59 wt % of butadiene unitsand 7 wt % of mono-n-butyl fumarate units.

To an autoclave, the above-produced latex and palladium catalyst (amixed solution of equivalent weights of ion-exchanged water and acetonesolution of 1 wt % palladium acetate) were added so as to have palladiumcontent of 1000 ppm to dry weight of the rubber included in the obtainedlatex, followed by performing hydrogenation reaction at hydrogenpressure of 3 MPa at a temperature of 50° C. for 6 hours, so that anitrile group containing highly-saturated copolymer rubber latex wasobtained.

The obtained nitrile group containing highly-saturated copolymer rubberlatex was added with twice volume of methanol. After solidification, thenitrile group containing highly-saturated copolymer rubber wasvacuum-dried at 60° C. for 12 hours to obtain a nitrile rubber (A1-1).Iodine value of the nitrile rubber (A1-1) was 10, the carboxyl groupcontent was 4.2×10⁻² ephr, and Mooney viscosity [ML₁₊₄ (100° C.)] was48.

Production Example 1-2

Except for not using mono-n-butyl fumarate, and with using 37 parts ofacrylonitrile and 63 parts of butadiene, a latex of anacrylonitrile-butadiene copolymer rubber, comprising 37 wt % ofacrylonitrile units and 63 wt % of butadiene units, was obtained by thesame procedures as in the production example 1-1. Then, as for theobtained rubber, hydrogenation reaction was carried out as with theproduction example 1-1 to prepare a nitrile rubber (A1′-2). Iodine valueof the nitrile rubber (A1′-2) was 10, and Mooney viscosity [ML₁₊₄ (100°C.)] was 65.

Example 1-1

By using a Bambury mixer, 100 parts of the nitrile rubber (A1-1), 1 partof stearic acid, 40 parts of FEF carbon black (Asahi 60 manufactured byAsahi Carbon Co., Ltd.), 5 parts of plasticizer (ADEKA CIZER C-8manufactured by Asahi Denka Company Limited) and 2 parts ofN-isopropyl-N′-phenyl-p-phenylene diamine (NOCRAC 810NA manufactured byOuchi Shinko Chemical Industrial, an aromatic secondary amine-basedanti-aging agent (A2-1)) were mixed. Then, the obtained mixture wastransferred to a roll and added with 2 parts of 1,3-di-o-tolylguanidine(NOCCELER DT manufactured by Ouchi Shinko Chemical Industrial, acrosslinking accelerator) and 3.4 parts of hexamethylene diaminecarbamate (Diak#1 manufactured by DuPont Dow Elastomers L.L.C., apolyamine-based crosslinking agent (A3-1)) to knead, so that acrosslinkable rubber composition with compound Mooney viscosity of 96was prepared.

The cross-linked rubber obtained by cross-linking the above preparedcrosslinkable rubber composition was subject to each test and evaluationof normal physical properties, properties after secondary cross-link andO-ring set test (150° C., 504 hours). The results are shown in Table 1.

Examples 1-2 to 1-4

Except for using each anti-aging agent shown in Table 1 instead ofN-isopropyl-N′-phenyl-p-phenylene diamine (A2-1), a crosslinkable rubbercomposition was respectively prepared by the same procedures as in theexample 1-1.

Namely, in the example 1-2, octylated diphenylamine [NOCRAC AD-Fmanufactured by Ouchi Shinko Chemical Industrial, an aromatic secondaryamine-based anti-aging agent (A2-2)],

in the example 1-3, 4,4′-bis(α,α′-dimethylbenzil)diphenylamine [NOCRACCD manufactured by Ouchi Shinko Chemical Industrial, an aromaticsecondary amine-based anti-aging agent (A2-3)], and

in the example 1-4, styrenated diphenylamine [NONFLEX LAS manufacturedby Seiko Chemical Co., Ltd., an aromatic secondary amine-basedanti-aging agent (A2-4)]

were respectively used.

Example 1-5

As shown in Table 1, except for using 8.6 parts of2,2-bis[4-(4-aminophenoxy)phenyl]propane [BAPP manufactured by WakayamaSeika Kogyo Co., Ltd., a polyamine-based crosslinking agent (A3-2)] as acrosslinking agent instead of hexamethylene diamine carbamate (A3-1), acrosslinkable rubber composition was prepared by the same procedures asin the example 1-1.

Comparative Example 1-1

Except for not using N-isopropyl-N′-phenyl-p-phenylene diamine (A2-1) asan anti-aging agent, a crosslinkable rubber composition was prepared bythe same procedures as in the example 1-1.

Comparative Examples 1-2 to 1-5

Except for using each anti-aging agent shown in Table 1 instead ofN-isopropyl-N′-phenyl-p-phenylene diamine (A2-1) as an anti-aging agent,each crosslinkable rubber composition was prepared by the sameprocedures as in the example 1-1.

Namely, in the comparative example 1-2,2,2,4-trimethyl-1,2-dihydroquinoline [NOCRAC 224 manufactured by OuchiShinko Chemical Industrial, (A2′-5)],

in the comparative example 1-3, 2-mercaptobenzimidazole [NOCRAC MBmanufactured by Ouchi Shinko Chemical Industrial, (A2′-6)],

in the comparative example 1-4, tris(nonylphenyl)phosphite [NOCRAC TNPmanufactured by Ouchi Shinko Chemical Industrial, (A2′-7)], and

in the comparative example 1-5, 4,4′-thio bis(3-methyl-6-t-butylphenol)[NOCRAC 300 manufactured by Ouchi Shinko Chemical Industrial, (A2′-8)]

were respectively used.

Comparative Examples 1-6

Except for adding 8 parts of 1,3-bis(t-butylperoxyisopropyl)benzene[Vulcup 40KE manufactured by Hercules Inc., (A3′-3)] instead ofhexamethylene diamine carbamate (A3-1) as a crosslinking agent, and notadding 3-di-o-tolylguanidine, a crosslinkable rubber composition wasprepared by the same procedures as in the example 1-1.

Comparative Example 1-7

Except for using the above produced nitrile rubber (A1′-2) instead ofthe nitrile rubber (A1-1), a crosslinkable rubber composition wasprepared by the same procedures as in the example 1-1.

TABLE 1 Comparative Examples Examples 1-1 1-2 1-3 1-4 1-5 1-1 1-2Included Nitrile rubber (A1-1) (A1-1) Antioxidant (A2-1) (A2-2) (A2-3)(A2-4) (A2-1) — (A2′-5) Cross-linking agent (A3-1) (A3-2) (A3-1)Test/Evaluation Compound Mooney viscosity 96 93 96 100 84 101 98 [ML₁₊₄,100° C.] Normal Tensile strength (MPa) 20.9 18.9 18.8 20.3 18.6 19.219.2 physical Elongation (%) 210 200 190 200 240 210 200 properties 100%tensile stress (MPa) 9.0 8.1 9.1 9.4 9.2 8.5 8.8 Properties Tensilestrength (MPa) 21.7 21.1 21.9 21.8 21.8 21.3 20.4 after Elongation (%)180 170 170 170 210 170 160 secondary 100% tensile stress (MPa) 11.111.1 11.4 11.9 9.1 11.4 11.2 cross-link O-ring compression set 67 70 6868 69 81 77 (150° C., 504 hours) (%) Comparative Examples 1-3 1-4 1-51-6 1-7 Included Nitrile rubber (A1-1) (A1′-2) Antioxidant (A2′-6)(A2′-7) (A2′-8) (A2-1) (A2-1) Cross-linking agent (A3-1) (A3′-3) (A3-1)Test/Evaluation Compound Mooney viscosity 97 97 101 77 85 [ML₁₊₄, 100°C.] Normal Tensile strength (MPa) 21.5 19.5 20.1 21.5 unvulcanizedphysical Elongation (%) 210 210 210 340 properties 100% tensile stress(MPa) 8.7 7.8 8.5 5.8 Properties Tensile strength (MPa) 20.7 19.8 19.921.0 after Elongation (%) 180 160 160 290 secondary 100% tensile stress(MPa) 10.7 11.2 11.5 6.2 cross-link O-ring compression set 88 76 79 100(150° C., 504 hours) (%) (NOTE) (A2-1):N-isopropyl-N′-phenyl-p-phenylene diamine (NOCRAC 810NA manufactured byOuchi Shinko Chemical Industrial) (A2-2): octylated diphenylamine(NOCRAC AD-F manufactured by Ouchi Shinko Chemical Industrial) (A2-3):4,4′-bis(α,α′-dimethylbenzil)diphenylamine (NOCRAC CD manufactured byOuchi Shinko Chemical Industrial) (A2-4): styrenated diphenylamine(NONFLEX LAS manufactured by Seiko Chemical Co., Ltd.) (A2′-5):2,2,4-trimethyl-1,2-dihydroquinoline (NOCRAC 224 manufactured by OuchiShinko Chemical Industrial) (A2′-6): 2-mercaptobenzimidazole (NOCRAC MBmanufactured by Ouchi Shinko Chemical Industrial) (A2′-7): tris (nonylphenyl)phosphite (NOCRAC TNP manufactured by Ouchi Shinko ChemicalIndustrial) (A2′-8): 4,4′-thiobis(3-methyl-6-t-butylphenol (NOCRAC 300manufactured by Ouchi Shinko Chemical Industrial) (A3-1): hexamethylenediamine carbamate (Diak#1 manufactured by DuPont Dow Elastomers L.L.C.)(A3-2): 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP manufactured byWakayama Seika Kogyo Co., Ltd.) (A3′-3):1,3-bis(t-butylperoxyisopropyl)benzene (Vulcup 40KE manufactured byHercules Inc.)

Evaluation of Examples and Comparative Examples According to the FirstAspect

As shown in Table 1, any crosslinkable rubber composition, comprisingthe nitrile rubber (A1-1) including acrylonitrile monomer unit andmono-n-butyl fumarate monomer unit and having iodine value of 10, anyone of aromatic secondary amine-based anti-aging agents (A2-1) to (A2-4)and any one of polyamine-based crosslinking agents (A3-1) and (A3-2), iseasy to handle since the compound Mooney viscosity is as low as 120 orless; is well-balanced in mechanical strength, such as tensile strengthand tensile stress, and elongation; and has particularly small O-ringcompression set (70% or less) (examples 1-1 to 1-5).

On the other hand, (i) when not adding an anti-aging agent to thenitrile rubber (A1-1); alternatively adding quinoline derivative based(A2′-5), sulfur compound based (A2′-6), phosphorus compound based(A2′-7), or polyphenol derivative based (A2′-8) anti-aging agent andcross-linking by the polyamine-based crosslinking agent (A3-1)(comparative examples 1-1 to 1-5), and

(ii) when using aromatic secondary amine-based anti-aging agent (A2-1)to the nitrile rubber (A1-1) and organic peroxide based crosslinkingagent (A3′-3) (comparative example 1-6),

all of the obtained cross-linked rubbers showed large O-ring compressionset (76% or more), so that compression set was deteriorated.

Also, some cases showed excellent mechanical strength but ill-balancedto elongation (comparative examples 1-2, 1-4 and 1-5); others showedenormously-lowered 100% tensile stress (comparative example 1-6). Thecomparative examples 1-1 and 1-3 were well-balanced in mechanicalstrength and elongation but further deteriorated in compression set.

Further, it was impossible to cross-link the rubber composition obtainedby using the nitrile rubber (A1′-2), not satisfying requirements of thenitrile rubber (A1) in the present invention, even when using thearomatic secondary amine-based anti-aging agent (A2-1) andpolyamine-based crosslinking agent (A3-1) (comparative example 1-7).

Examples and Comparative Examples According to the Second Aspect

Next, examples according to the second aspect (examples 2-1 to 2-2) andcomparative examples (comparative examples 2-1 to 2-4) will bedescribed. Note that in the examples and comparative examples accordingto the second aspect, each of the tests (1) to (4) and evaluation, as inthe above first aspect, and each of the following tests (9) to (11) andevaluation were carried out.

(9) Mooney Scorch Test

From a result of measurement according to JIS K6300-1 at a temperatureof 125° C. by using an L-shaped rotor, Mooney scorch time t5 (minute)and a lowest value Vmin of Mooney viscosity [ML₁₊₄ (100° C.)] wereobtained. The larger t5 (minute) results in the superior scorchstability. Also, it is considered that the lower Vmin results in thesuperior workability at molding.

(10) Normal Physical Property (Hardness)

The crosslinkable rubber composition was cross-linked at 170° C. for 20minutes at a pressure of 10 MPa to produce a pressed cross-linked testspecimen. After secondary cross-link at 170° C. for 4 hours, hardness ofthe obtained cross-linked rubber was measured according to JIS K6253 byusing a durometer hardness tester type A.

(11) O-Ring Set Test (150° C., 168 Hours)

By using a mold with an internal diameter of 30 mm and a ring diameterof 3 mm, the crosslinkable rubber composition was cross-linked at 170°C. for 20 minutes at a pressure of 10 MPa, followed by secondarycross-link at 170° C. for 4 hours to obtain a test specimen for O-ringset test. Then, O-ring compression set was measured according to JISK6262 under a condition of compressing a distance of two planessandwiching an O-ring by 25% in a ring thickness direction at 150° C.for 168 hours.

Example 2-1

First, a nitrile rubber (B1-1) was prepared by the same productionmethod employed for the nitrile rubber (A1-1) in the above productionexample 1-1.

Next, by using a Bambury mixer, 100 parts of nitrile rubber (B1-1), 1part of stearic acid, 40 parts of carbon black (N550 by Tokai CarbonCo., Ltd.), 0.5 part of octadecylamine (Farmin 80 by Kao ChemicalCompany, a primary monoamine having no polar group other than an aminogroup), 5 parts of trimellitic acid ester (ADEKA CIZER C-8, aplasticizer manufactured by Asahi Denka Company Limited), 1.5 parts of4,4′-di-(α,α′-dimethylbenzil)diphenylamine (Naugard 445 manufactured byUniroyal Inc., an anti-aging agent) and 1.5 parts of2-mercaptobenzimidazole (NOCRAC MB manufactured by Ouchi Shinko ChemicalIndustrial, an anti-aging agent) were mixed. Then, the obtained mixturewas transferred to a roll and added with 2 parts of1,3-di-o-tolylguanidine (NOCCELER DT manufactured by Ouchi ShinkoChemical Industrial, a crosslinking accelerator) and 3 parts ofhexamethylene diamine carbamate (Diak#1 manufactured by DuPont DowElastomers L.L.C., a polyamine-based crosslinking agent) to knead, sothat a crosslinkable rubber composition with compound Mooney viscosityof 92 was prepared.

In addition to Mooney scorch test of the above prepared crosslinkablerubber composition, each test and evaluation of normal physical propertyand O-ring set test (150° C., 168 hours) of the cross-linked rubberobtained by cross-linking the crosslinkable rubber composition wascarried out. The results are shown in Table 2.

Example 2-2 and Comparative Example 2-1

Except for changing an amount of octadecylamine from 0.5 part in example2-1 into 1 part (example 2-2), or zero (comparative example 2-1), acrosslinkable rubber composition was respectively prepared by the sameprocedures as in the example 2-1 as well as same tests and evaluations.The results are shown in Table 2.

Comparative Examples 2-2 and 2-3

Except for using 2 parts of dialkylamine (Armeen 2C by Lion Akzo Co.,Ltd., 8 to 18 of carbon number of an alkyl group) (comparative example2-2), or 1 part of n-butyl aldehyde aniline (comparative example 2-3)instead of using 0.5 parts of octadecylamine as in the example 2-1, acrosslinkable rubber composition was respectively prepared by the sameprocedures as in the example 2-1 as well as same tests and evaluations.The results are shown in Table 2.

Comparative Example 2-4

First, a nitrile rubber (B1′-2), produced by the same method as withnitrile rubber (A1′-2) in the above production example 1-2, wasprepared.

Then, a crosslinkable rubber composition was respectively prepared bythe same procedures as in the example 2-1 as well as same tests andevaluations, except for using 100 parts of nitrile rubber (B1′-2)instead of 100 parts of nitrile rubber (B1-1); and for peroxidecross-link instead of that between carboxyl groups, further using 12parts of 1,3-bis(t-butylperoxyisopropyl)benzene (Vulcup 40KEmanufactured by Hercules Inc., concentration 40 wt %) instead of 3 partsof hexamethylene diamine carbamate and 4 parts ofN,N-m-phenylenedimaleimide (HVA-2 manufactured by DuPont Dow ElastomersL.L.C.) instead of 2 parts of 1,3-di-o-tolylguanidine as a crosslinkingaccelerator. The results are shown in Table 2.

TABLE 2 Examples Comparative Examples 2-1 2-2 2-1 2-2 2-3 2-4 Included(parts) nitrile rubber (B1-1) 100 100 100 100 100 — nitrile rubber(B1′-2) — — — — — 100 octadecylamine 0.5 1 — — — 0.5 dialkylamine — — —2 — — n-butyl aldehyde aniline — — — — 1 — hexamethylene diaminecarbamate 3 3 3 3 3 — 1,3-di-o-tolylguanidine 2 2 2 2 2 —1,3-bis(t-butyl peroxy isopropyl)benzene (40 wt %) — — — — — 12N,N-m-phenylenedimaleimide — — — — — 4 Compound Mooney viscosity [ML₁₊₄,100° C.] 92 87 117 114 111 87 Mooney t5 (min) 8.7 9.9 7.5 7.9 7.8 19.5scorch Vmin [ML₁₊₄, 100° C.] 52 48 77 80 75 48 Normal Tensile strength(MPa) 18.2 17.8 19.1 16.8 18.3 26.0 physical Elongation (%) 170 170 160150 150 75 properties Hardness (Duro A) 73 73 73 73 74 75 O-ringcompression set 56 55 52 56 55 77 (150° C., 168 hours) (%)

Evaluation of Examples and Comparative Examples According to the SecondAspect

As shown in Table 2, the crosslinkable rubber compositions containingthe nitrile rubber (B1-1) including an acrylonitrile unit and amono-n-butyl fumarate unit and having iodine value of 10, and primarymonoamine (B2) and polyamine-based crosslinking agent (B3) predefined inthe present invention (invention according to the second aspect) can allprovide a cross-linked rubber (examples 2-1 and 2-2), low in compoundMooney viscosity as low as 100 or less; sufficiently long in scorch timet5; easy to handle because of low Vmin; as well as showing sufficienttensile strength and elongation, and small O-ring compression set as lowas 60% or less.

On the other hand, the crosslinkable rubber composition not containingthe primary monoamine (B2) predefined in the present invention(invention according to the second aspect) and the crosslinkable rubbercomposition containing a dialkylamine or a mono amine having polar groupinstead of the primary monoamine (B2) predefined in the presentinvention (invention according to the second aspect) result in highcompound Mooney viscosity and Vmin, short scorch time t5, and inferiorworkability (comparative examples 2-1 to 2-3). Even when blending theprimary monoamine (B2) and polyamine-based crosslinking agent (B3)predefined in the present invention (invention according to the secondaspect), the use of peroxide as a crosslinking agent to nitrile rubberhaving no carboxyl group results in the obtained cross-linked rubberswith increased O-ring compression set (comparative examples 2-4).

Examples and Comparative Examples According to the Third Aspect

Next, a production example (production example 3-1), examples (examples3-1 to 3-2) according to the third aspect and comparative examples(comparative examples 3-1 to 3-4) will be described. Note that in theexamples and comparative examples according to the third aspect, each ofthe tests (1) to (3) and (6) and evaluation as in the above firstaspect, and each of the following tests (12) to (15) and evaluation werecarried out.

(12) Roll Adherence Property

Roll adherence property was evaluated in 6 standards in which 4 stepswere added between the following two standards based on the conditionsduring the roll-kneading operation to:

0: shows intense roll adherence property and is impossible to bekneaded;

5: shows no roll adherence property and is easy to be kneaded.

(13) Normal Physical Property (Hardness) After Secondary Cross-Link

The crosslinkable rubber composition was placed in a mold with a lengthof 15 cm, a width of 15 cm and a depth of 0.2 cm, cross-linked at 170°C. for 20 minutes at a pressure of 10 MPa followed by secondarycross-link in a gear oven at 170° C. for 4 hours to produce a testspecimen. In accordance with JIS K6253, hardness of the cross-linkedrubber after the secondary cross-link was measured by using a durometerhardness tester type A.

(14) O-Ring Set Test (170° C., 70 Hours)

By using a mold with an internal diameter of 30 mm, a ring diameter of 3mm and a depth of 3 mm, the crosslinkable rubber composition wascross-linked at 170° C. for 20 minutes at a pressure of 10 MPa, followedby secondary cross-link at 170° C. for 4 hours to obtain a test specimenfor O-ring set test. Then, O-ring compression set was measured accordingto JIS K6262 under a condition of compressing a distance of two planessandwiching an O-ring by 25% in a ring thickness direction at 170° C.for 70 hours.

(15) Heat Aging Resistance Test (170° C., 168 Hours)

As for the test specimen obtained by primary and secondary cross-link asin the above (13), tensile strength and its rate of change (%) as wellas elongation and its rate of change (%) were measured after keeping itat 170° C. for 168 hours according to JIS K6257 (normal oven method).

Production Example 3-1

Except for changing amounts of t-dodecylmercaptan (molecular weightmodifier) from 0.5 part to 0.7 part, and of Cumene hydroperoxide(polymerization catalyst) from 0.1 part to 0.06 part, was obtained aswith the production example 1-1, a latex (solid content concentration ofabout 25 wt %) of an acrylonitrile-butadiene-α,β-ethylenicallyunsaturated dicarboxylic monoalkyl ester copolymer rubber containing 35wt % of acrylonitrile unit, 57.8 wt % of butadiene unit and 7.2 wt % ofmono-n-butyl fumarate unit.

Next, the obtained rubber was subject to hydrogenation reaction as inthe production example 1-1, so that a highly-saturated nitrile rubber(C1-1) was obtained. Iodine value of the highly-saturated nitrile rubber(C1-1) was 7, carboxyl group content was 4.2×10⁻² ephr, and Mooneyviscosity [ML₁₊₄ (100° C.)] was 50.

Example 3-1

By using a Bambury mixer, 100 parts of the highly-saturated nitrilerubber (C1-1) was added with 1 part of polyoxyethylene alkyl etherphosphate ester (product name: “Phosphanol RL-210” manufactured by TOHOChemical Industry Co., Ltd.; including 41.6 wt % of monoesters, 38.4 wt% of diesters and about 20 wt % of polyoxyethylene alkyl ethers), 1.5parts of 4,4′-di-(α,α′-dimethylbenzil)diphenylamine (Naugard 445manufactured by Uniroyal Inc., an anti-aging agent) and 40 parts of FEFcarbon black (Asahi 60 manufactured by Asahi Carbon Co., Ltd., areinforcing filler) and mixed. Next, the obtained mixture wastransferred to a roll and 2 parts of 3-di-o-tolylguanidine (NOCCELER DTmanufactured by Ouchi Shinko Chemical Industrial, a crosslinkingaccelerator) and 3.4 parts of hexamethylene diamine carbamate [Diak#1manufactured by DuPont Dow Elastomers L.L.C., a polyamine-basedcrosslinking agent] were added and kneaded to prepare a crosslinkablerubber composition.

Each test and evaluation was performed for roll adherence property atpreparation of the above prepared crosslinkable rubber composition,normal physical property of the cross-linked rubber obtained bycross-linking of the crosslinkable rubber composition, O-ring set test(170° C., 70 hours) and heat aging resistance (170° C., 168 hours). Theresults are shown in Table 3.

Example 3-2

Except for replacing 1 part of polyoxyethylene alkyl ether phosphateester with 1 part of polyoxyethylene octadecylether phosphate ester(product name “VAMFRE VAM” manufactured by R.T. Vanderbilt CompanyInc.), a crosslinkable rubber composition was obtained by the sameprocedures as in the example 3-1 as well as same tests and evaluations.The results are shown in Table 3.

Comparative Example 3-1

Except for not adding polyoxyethylene alkyl ether phosphate ester, acrosslinkable rubber composition was obtained by the same procedures asin the example 3-1 as well as same tests and evaluations. The resultsare shown in Table 3.

Comparative Examples 3-2 to 3-4

Except for replacing 1 part of polyoxyethylene alkyl ether phosphateester in the example 3-1 with 1 part each of stearic acid (comparativeexample 3-2), fatty acid ester (comparative example 3-3) or phosphoricacid tri(2-ethylhexyl)ester (comparative example 3-4), a crosslinkablerubber composition was respectively obtained by the same procedures asin the example 3-1. Note that as the fatty acid ester (comparativeexample 3-3), product name “Structol WB222” manufactured by StructolCompany; and as the phosphoric acid tri(2-ethylhexyl)ester (comparativeexample 3-4), product name “TOP” manufactured by Daihachi ChemicalIndustry Co., Ltd.; were respectively used.

Each of the above obtained crosslinkable rubber composition was subjectto same tests and evaluation as in the example 3-1. The results areshown in Table 3.

TABLE 3 Examples Comparative Examples 3-1 3-2 3-1 3-2 3-3 3-4 Included(parts) Phosphanol RL-210 *1 1 — — — — — VAMFRE VAM *2 — 1 — — — —stearic acid — — — 1 — — Structol WB222 (fatty acid ester) *3 — — — — 1— phosphoric acid tri(2-ethylhexyl)ester — — — — — 1 Test results Rolladherence property 5 5 2 4 3 2 Normal Tensile strength (MPa) 21.6 21.021.0 21.7 21.5 22.0 physical Elongation (%) 150 140 140 150 140 160properties Hardness (Duro A) 78 78 79 78 78 77 O-ring set test 33 32 4442 45 43 (170° C., 70 hours) (%) Heat aging Tensile strength - change ofrate (%) +6 +8 −34 −41 −39 −16 resistance Elongation - change of rate(%) −24 −18 −50 −56 −52 −41 Hardness - degree of change +4 +4 +6 −7 +7+6 *1: product of TOHO Chemical Industry Co., Ltd. *2: product of R.T.Vanderbilt Company Inc. *3: product of Structol Company

Evaluation of Examples and Comparative Examples According to the ThirdAspect

As shown in Table 3, the predefined crosslinkable rubber composition ofthe present invention (invention according to the third aspect) are allsmall in roll adherence property and easy to handle, good in tensilestrength, elongation and hardness of the cross-linked rubber, andsignificantly small in O-ring compression set as low as 35% or less; andin addition, they can provide cross-linked rubbers excellent in heataging resistance (examples 3-1 and 3-2).

On the other hand, when not adding polyoxyethylene alkyl ether phosphateester, or replacing polyoxyethylene alkyl ether phosphate ester with 1part each of stearic acid, fatty acid ester or phosphoric acidtri(2-ethylhexyl)ester, the crosslinkable rubber compositions are allstrong in roll adherence property and bad in kneading workability. Also,the obtained cross-linked rubbers are all large in O-ring compressionset, resulting in inferior heat aging resistance (comparative examples3-1 to 3-4).

Examples and Comparative Examples According to the Fourth Aspect

Next, production examples (production examples 4-1 to 4-2), examples(example 4-1 to 4-3) according to the fourth aspect and comparativeexamples (comparative examples 4-1 to 4-3) will be described. Note thatin the examples and comparative examples according to the fourth aspect,the following test (16) and evaluation were carried out in addition toeach of the tests (1) to (3) and (6) and evaluation in the above firstaspect, and the test (11) and evaluation of the above second aspect.

(16) Heat Aging Resistance Test (150° C., 504 Hours)

The crosslinkable rubber composition was placed in a mold with a lengthof 15 cm, a width of 15 cm and a depth of 0.2 cm, cross-linked at 170°C. for 20 minutes at a pressure of 10 MPa, followed by secondarycross-link in a gear oven at 170° C. for 4 hours to produce a testspecimen. The produced test specimen was kept at 150° C. for 504 hoursaccording to JIS K6257 (normal oven method), and then, tensile strengthand its rate of change (%) as well as elongation and its rate of change(%) were measured.

Production Example 4-1

200 parts of ion-exchanged water, 3 parts of sodium lauryl sulfate(emulsifier), 70 parts of ethyl acrylate, 28 parts of n-butyl acrylateand 2 parts of monomethyl maleate were added into a polymerizationreactor equipped with a thermometer and a stirring device, and afterrepeating deaerating decompression and nitrogen substitution twice tosufficiently remove oxygen, 0.005 part of cumene hydroperoxide and 0.002part of sodium formaldehyde sulfoxylate were added to initiate emulsionpolymerization at a normal pressure at a temperature of 30° C. Thereaction was continued until polymerization conversion ratio reached95%. The obtained emulsion polymerization solution was solidified with acalcium chloride solution, followed by dewatering, water washing anddrying, to obtain an acrylic rubber (D2-1).

The composition of the acrylic rubber (D2-1) was 70 wt % of ethylacrylate unit, 28 wt % of n-butyl acrylate unit and 2 wt % of monomethylmaleate unit (carboxyl group content of 1.3×10⁻² ephr); and Mooneyviscosity [ML₁₊₄ (100° C.)] was 45.

Production Example 4-2

Except for changing amounts of ethyl acrylate and n-butyl acrylate addedinto the polymerization reactor from 70 parts to 30 parts and from 28parts to 35 parts respectively, and replacing 2 parts of monomethylmaleate with 33 parts of 2-methoxyethyl acrylate and 2 parts ofmethacrylic acid, an acrylic rubber (D2′-2) was obtained as with theproduction example 4-1.

The composition of the acrylic rubber (D2′-2) was 30 wt % of ethylacrylate, 35 wt % of n-butyl acrylate, 33 wt % of 2-methoxyethylacrylate and 2 wt % of methacrylic acid; and Mooney viscosity [ML₁₊₄,(100° C.)] was 35.

Example 4-1

First, a nitrile rubber (D1-1), produced by the same method as with thenitrile rubber (A1-1) in the above production example 1-1, was prepared.

Then, by using a Bambury mixer, 75 parts of the nitrile rubber (D1-1)and 25 parts of the above produced acrylic rubber (D2-1) were added with1 part of stearic acid, 40 parts of FEF carbon black (Asahi 60manufactured by Asahi Carbon Co., Ltd.), 5 parts of a plasticizer (ADEKACIZER C-8 manufactured by Asahi Denka Company Limited), 0.5 part of anorganic acid resin complex-based lubricant (Moldwiz 21G manufactured byTomoe Engineering Co., Ltd.), 1 part of ester-based wax (GREG G8205manufactured by Dainippon Ink and Chemicals, Incorporated), 1.5 parts ofan amine-based anti-aging agent (Naugard 445 manufactured by UniroyalInc.) and 1.5 parts of 2-mercaptobenzimidazole (NOCRAC MB manufacturedby Ouchi Shinko Chemical Industrial, an anti-aging agent) and mixed.Then, the obtained mixture was transferred to a roll and added with 2parts of 1,3-di-o-tolylguanidine (NOCCELER DT manufactured by OuchiShinko Chemical Industrial, a basic crosslinking accelerator) and 2.7parts of hexamethylene diamine carbamate (Diak#1 manufactured by DuPontDow Elastomers L.L.C., a polyamine-based crosslinking agent) to knead,so that a crosslinkable rubber composition with compound Mooneyviscosity of 72 was obtained.

The cross-linked rubber obtained by cross-linking the above preparedcrosslinkable rubber composition was subject to each test and evaluationof properties after secondary cross-link, heat aging resistance (150°C., 504 hours) and O-ring set test (150° C., 168 hours). The results areshown in Table 4.

Examples 4-2 and 4-3, and Comparative Example 4-1

Except for changing a compounding ratio of the nitrile rubber (D1-1) andacrylic rubber (D2-1) and an amount of hexamethylene diamine carbamateto those shown in Table 4, a crosslinkable rubber composition wasrespectively obtained by the same procedures as in the example 4-1 aswell as same tests and evaluations. The results are shown in Table 4.

Comparative Example 4-2

Except for changing an amount of the nitrile rubber (D1-1) from 75 partsto 50 parts, replacing 25 parts of acrylic rubber (D2-1) with 50 partsof acrylic rubber (D2′-2), and changing an amount of the hexamethylenediamine carbamate from 2.7 parts to 2.1 parts, a crosslinkable rubbercomposition was obtained by the same procedures as in the example 4-1 aswell as same tests and evaluations. The results are shown in Table 4.

Comparative Example 4-3

Except for changing amounts of the nitrile rubber (D1-1) and acrylicrubber (D2-1) to 50 parts, and replacing 1,3-di-o-tolylguanidine andhexamethylene diamine carbamate with 8 parts of1,3-bis(t-butylperoxyisopropyl)benzene of 40% product (Vulcup 40KE byGEO Specialty Chemicals Inc., an organic peroxide) (3.2 parts in termsof pure organic peroxide), a crosslinkable rubber composition wasobtained by the same procedures as in the example 4-1 as well as sametests and evaluations. The results are shown in Table 4.

TABLE 4 Comparative Examples Examples 4-1 4-2 4-3 4-1 4-2 4-3 Included(parts) rubber (D1-1) 75 50 25 100 50 50 rubber (D2-1) 25 50 75 — — 50rubber (D2′-2) — — — — 50 — hexamethylene diamine carbamate 2.7 2.1 1.43.4 2.1 — 1,3-bis(t-butyl peroxy isopropyl)benzene (40 wt %) — — — — — 8Compound Mooney viscosity [ML₁₊₄, 100° C.] 72 57 43 92 60 52 PropertiesTensile strength (MPa) 17.4 13.4 11.0 20.1 14.6 16.2 after Elongation(%) 190 180 180 190 230 240 secondary cross-link Heat aging Tensilestrength (MPa) 15.7 14.3 10.9 15.4 13.8 15.0 test Elongation (%) 110 120140 90 120 160 Tensile strength - change of rate (%) −10 7 −1 −23 −5 −7Elongation - change of rate (%) −42 −33 −22 −53 −48 −33 O-ringcompression setz 36 30 23 44 70 78 (150° C., 168 hours) (%)

Evaluation of Examples and Comparative Examples According to the FourthAspect

As shown in Table 4, the predefined crosslinkable rubber compositions ofthe present invention (invention according to the fourth aspect) are alllow in compound Mooney viscosity as low as 80 or less and easy tohandle, and can provide a cross-linked rubber with sufficiently largetensile strength as high as 10 MPa or more; no particular troubles inheat aging test except for reduction in elongation; and significantlysmall O-ring compression set as low as 40% or less (examples 4-1 to4-3).

On the other hand, the use of the nitrile rubber (D1-1) as an onlyrubber results in reduced elongation in heat aging test and increasedcompression set (comparative example 4-1). Also, when mixing the nitrilerubber (D1-1) and acrylic rubber (D2-1) by 50 parts/50 parts, the rubbercomposition using an organic peroxide as a crosslinking agent results inlarge O-ring compression set as high as 70% or more (comparative example4-3).

Also, even when using the acrylic rubber (D2′-2) containing anα,β-ethylenically unsaturated mono carboxylic acid monomer unit but noα,β-ethylenically unsaturated dicarboxylic acid monoester monomer unitas an acrylic rubber, the cross-linked rubber of the rubber compositionshows large O-ring compression set which is 70% (comparative example4-2).

The invention claimed is:
 1. A crosslinkable rubber compositioncomprising 0.2 to 10 parts by weight of an aromatic secondaryamine-based anti-aging agent and 0.2 to 20 parts by weight of apolyamine-based crosslinking agent with respect to 100 parts by weightof a nitrile rubber, wherein said nitrile rubber has an iodine value of25 or less and includes as monomer units an α,β-ethylenicallyunsaturated nitrile monomer unit, 45 to 75 weight-% of a conjugateddiene-based monomer unit per 100 weight-% of total monomers units, andan α,β-ethylenically unsaturated dicarboxylic acid monoester monomerunit, in which a monomer forming said α,β-ethylenically unsaturateddicarboxylic acid monoester monomer unit is a monoester monomer of adicarboxylic acid containing a carboxyl group in each of two carbonatoms forming an α,β-ethylenically unsaturated bond; and wherein saidcrosslinkable rubber composition is capable of providing a cross-linkedrubber wherein O-ring compression set is 71% or less after maintainingthe cross-linked rubber in a 25%-compressed state at 150° C. for 504hours.
 2. The crosslinkable rubber composition as set forth in claim 1,wherein compound Mooney viscosity ML₁₊₄ (100° C.) is 15 to
 200. 3. Across-linked rubber obtained by cross-linking the crosslinkable rubbercomposition as set forth in claim
 1. 4. The cross-linked rubber as setforth in claim 3, which is a seal material.
 5. The cross-linked rubberas set forth in claim 3, which is a belt material.
 6. The crosslinkablerubber composition as set forth in claim 1, wherein said monomer formingsaid α,β-ethylenically unsaturated dicarboxylic acid monoester monomerunit is a monoalkylester of maleic acid or a monoalkyl ester of fumaricacid.
 7. The crosslinkable rubber composition as set forth in claim 1,wherein said conjugated diene-based monomer unit is a 1,3-butadieneunit.
 8. The crosslinkable rubber composition as set forth in claim 1,wherein said nitrile rubber is a hydrogenated rubber.
 9. Thecrosslinkable rubber composition as set forth in claim 7, wherein saidnitrile rubber is a hydrogenated rubber.